BIOLOGY 


A  COURSE  IN 
VERTEBRATE  ZOOLOGY 


A    GUIDE    TO    THE 

DISSECTION  AND    COMPARATIVE   STUDY 
OF  VERTEBRATE   ANIMALS 


BY 


HENRY    SHERRING    PRATT,  PH.D. 

PROFESSOR  OF  BIOLOGY  AT  HAVERFORD  COLLEGE  AND  INSTRUCTOR 

IN  COMPARATIVE  ANATOMY  AT  THE  MARINE  BIOLOGICAL 

LABORATORY  AT  COLD  SPRING  HARBOR,  L.I. 


GINN  &  COMPANY 

BOSTON  •  NEW  YORK  •  CHICAGO  •  LONDON 


COPYRIGHT,  1905,  BY 
HENRY  SHEERING  PRATT 

ALL  BIGHTS  RESERVED 
39.4 


fltftenatum 


GINN  &  COMPANY  •  PRO- 
PRIETORS  •  BOSTON  .  U.S.A. 


PREFACE 


The  plan  of  this  course  is  similar  to  that  of  the  Inverte- 
brate Zoology  published  by  the  author  three  years  ago.  Its 
principal  aim  is  to  furnish  a  guide  to  the  dissection  of  types 
of  the  most  important  groups  of  vertebrates.  The  directions 
are  practical  in  character  and  are  designed  to  be  in  sufficient 
detail  to  enable  the  student  to  carry  on  his  work  intelligently 
and  profitably,  and  with  the  least  possible  waste  of  time  and 
material.  Vertebrates  are  large  animals  with  complex  systems 
of  organs,  and  it  is  impossible  for  a  young  student  to  dissect 
them  in  the  best  manner  unless  he  receive  full  instructions  at 
every  important  step ;  —  to  give  such  instructions  is  the  main 
purpose  of  this  book. 

The  course  also  seeks  to  keep  the  morphological  relations  of 
the  various  organs  and  systems  of  organs  constantly  before  the 
mind,  and  to  make  the  study  a  comparative  one. 

Each  of  the  dissections  is  complete  in  itself  and  is  not  depend- 
ent upon  any  of  the  others.  The  teacher  may  thus  give  his  class 
such  of  the  dissections  as  he  wishes,  and  in  the  order  he  wishes. 

The  directions  do  not  contain  exhaustive  descriptions  of  the 
animals  dissected,  the  completeness  of  the  description  in  each 
case  being  made  dependent  upon  the  pedagogical  ends  aimed 
at,  and  upon  the  time  ordinarily  at  the  disposal  of  the  student. 
The  organs  which  have  been  treated  in  the  least  detail  are  the 
muscles,  in  most  cases  only  the  superficial  ones  being  described, 
and  they  not  minutely.  A  teacher  will  find  it  an  easy  matter, 
however,  to  extend  the  study  of  the  muscles  if  he  wishes.  The 
particular  order  in  which  the  various  systems  of  organs  of  each 
animal  are  studied  is  the  one  which  experience  has  shown  will 
accomplish  the  desired  result  with  the  greatest  economy  of  time 
and  material. 

iii 

271618 


iv  PREFACE 

The  number  of  specimens  necessary  for  a  complete  dissec- 
tion is  mentioned  at  the  beginning  of  each  description.  In  most 
cases  one  specimen  is  needed  for  a  study  of  the  outer  form  and 
the  viscera,  including  the  heart  and  its  principal  vessels,  one 
specimen  for  the  complete  dissection  of  the  blood  vessels,  and 
one  for  the  skeleton.  In  case  material  is  scarce  or  expensive, 
however,  the  study  can  always  be  abbreviated  and  the  most 
important  organs  be  studied  with  a  single  specimen.  On  the 
other  hand,  if  material  be  abundant,  it  will  often  be  convenient 
to  use  more  than  the  number  of  specimens  mentioned. 

The  author  recognizes  the  great  importance  as  well  as  the 
great  difficulty  of  rendering  a  book  of  this  kind  free  from 
errors,  and  has  sought  to  accomplish  this  result  as  nearly  as 
possible.  To  all  who  have  assisted  and  advised  him  he  returns 
hearty  thanks ;  especially  to  Professor  Karl  Heider,  of  the  Uni- 
versity of  Innsbruck,  in  whose  laboratory  the  greater  part  of 
the  book  was  written.  He  will  also  be  under  the  greatest  obli- 
gation to  teachers  and  students  who  will  tell  him  of  any  mistakes 
of  fact  they  may  find,  or  of  improvements  which  may  suggest 
themselves  to  them.  H  g  PRATT 

HAVERFORD,  PENNSYLVANIA 
September,  1905 


CONTENTS 


INTRODUCTION 

APPARATUS vii 

DISSECTING  AND  DRAWING        .......  vii 

ANATOMICAL  TERMS    ........  viii 

MATERIALS  FOR  DISSECTION viii 

BOOKS  FOR  REFERENCE         .......  viii 

CLASSIFICATION  OF  VERTEBRATES x 

CHAPTER  I  — FISHES 

AN  ELASMOBRANCHIAN  FISH.     THE  DOGFISH      .         .         .         .  1 
A  TELEOSTEAN  FISH.     THE  PERCH         .         .         .         .         .         .33 

CHAPTER  II  — AMPHIBIANS 

A  URODELAN  AMPHIBIAN.     NECTURUS 65 

AN  ANURAN  AMPHIBIAN.     THE  FROG 94 

CHAPTER  III  — REPTILES 

A  TURTLE 135 

CHAPTER  IV  — BIRDS 

THE  PIGEON 166 

CHAPTER  V  — MAMMALS 

THE  CAT  213 


INDEX  .         .     281 


INTRODUCTION 


Apparatus.  Each  student  should  be  provided  with  the  follow- 
ing instruments  :  two  scalpels,  —  a  small  one  and  one  of  medium 
size ;  two  pairs  of  scissors',  —  a  large  straight  pair,  and  a  small 
pair  preferably  with  curved  tips  ;  two  pairs  of  forceps,  —  a  small 
and  a  large  pair,  both  straight  and  with  corrugated  tips;  two 
dissecting  needles,  a  probe,  a  blowpipe,  and  a  hand  lens.  There 
should  also  be  in  the  laboratory  at  the  disposal  of  the  class  one 
or  more  large  scalpels,  a  pair  of  bone  cutters,  a  small  saw,  and 
materials  for  making  injections. 

Each  student  should  have  a  large  dissecting  pan  —  in  the  bot- 
tom of  which  is  a  layer  of  black  wax  —  and  a  dissecting  board. 
He  should  also  have  a  number  of  strong  pins,  which  may  be 
conveniently  kept,  while  not  in  use,  stuck  in  a  large  cork. 

Dissecting  and  drawing.  Skill  in  dissecting  is  usually  quickly 
acquired  with  practice.  The  student  should  bear  in  mind  that 
dissection  does  not  mean  cutting  and  slashing,  but  the  care- 
ful separation  of  parts  in  order  that  they  may  be  studied.  He 
should  do  this  without  cutting,  when  possible,  and  when  he 
does  use  the  scalpel  and  scissors  he  should  do  it  slowly  and 
carefully,  and  always  know  exactly  what  he  is  about.  It  is 
also  important  that  the  scalpel,  forceps,  and  needle  be  held 
between  the  thumb  and  the  first  and  second  fingers,  like  a  pen, 
—  except  when  a  good  deal  of  force  must  be  exerted. 

The  drawings  must  be  clear  and  neat;  they  should  be  more 
or  less  diagrammatic,  and  should  be  made  with  a  hard  drawing 
pencil  in  a  large  blank  book,  the  paper  of  which  is  firm  and 
strong,  or  on  drawing  paper.  Previous  training  in  drawing  is 
not  necessary,  as  the  principal  object  of  the  drawings  is  to  show 
accurately  the  relations  of  the  various  parts  to  one  another,  and 
not  to  make  pictures.  Shading  should  usually  not  be  done,  and 


viii  INTRODUCTION 

all  the  lines  should  be  firm  and  definite.  The  use  of  colors  is 
often  helpful  in  drawing  complex  figures,  although  not  neces- 
sary; but  in  case  of  their  use  great  care  should  be  taken  that 
they  be  neatly  put  on,  as  the  careless  use  of  colors  invariably 
injures  the  drawing. 

Anatomical  terms.  No  particular  system  of  anatomical  nomen- 
clature has  been  employed  in  this  book,  such  terms  being  used 
as  would  make  the  descriptions  exact,  and  easy  to  understand. 
Anterior  and  posterior  indicate  the  direction  toward  the  front  and 
hind  ends  of  the  body,  respectively ;  dorsal,  the  direction  toward 
the  upper  side,  and  ventral  that  toward  the  under  side.  Lateral 
indicates  the  direction  away  from  the  middle,  longitudinal  plane 
of  the  body,  and  medial  the  direction  toward  that  plane.  Prox- 
imal and  distal  are  usually  applied  to  portions  of  an  extremity 
or  projection,  and  indicate  the  direction  toward  and  away  from 
its  base  or  attached  end,  respectively.  A  dorsoventral  plane  passes 
between  the  upper  and  the  under  surfaces  of  the  body, — the  sag- 
ittal plane  being  the  median,  longitudinal,  dorsoventral  plane. 

Materials  for  dissection.  The  dogfish  and  skate  may  be 
obtained,  already  injected  if  desired,  from  Dr.  F.  H.  Lambert, 
Tufts  College,  Massachusetts,  or  from  the  Supply  Department 
of  the  Biological  Laboratory,  Woods  Hole,  Massachusetts.  The 
perch  can  be  caught  in  any  fresh-water  stream  or  pond ;  it  can 
also  be  purchased  of  Brimley  Bros.,  Raleigh,  North  Carolina,  and 
often  at  fish  markets.  Necturus  can  be  obtained  of  Alexander 
Nielsen,  Venice,.  Ohio,  at  10  cents  apiece.  Frogs  are  easily  ob- 
tained, except  in  the  winter,  in  marshes  and  ponds,  or  they  can 
be  purchased  of  Brimley  Bros.  Turtles  may  be  caught  with  a 
small  net  in  ponds,  and  can  be  purchased  in  the  fish  markets  of  the 
larger  cities :  Upperman  Bros.,  1207  Filbert  Street,  Philadelphia, 
will  furnish  them.  Birds  and  cats  are  always  easy  to  obtain. 

Books  for  reference.  It  is  very  important  that  the  laboratory 
be  supplied  with  text-books  of  comparative  anatomy,  and  that 
the  dissections  be  supplemented  by  constant  reference  to  them, 
and  by  lectures  and  recitations.  The  two  best  text-books  in 
English  are  Kingsley's  Text-Book  of  Vertebrate  Zoology  (Holt) 
and  Wiedersheim's  Elements  of  the  Comparative  Anatomy  of 


INTEODUCTION  ix 

Vertebrates  (Macmillan).  The  former  treats  the  subject  from 
the  standpoint  of  embryology,  the  latter  from  that  of  the  adult 
structure.  The  former  has  the  advantage  of  being  an  American 
book  in  which  American  animals  are  used  by  way  of  illustra- 
tion wherever  possible,  and  also  of  containing  an  extended  out- 
line of  the  classification  of  vertebrates. 

More  exhaustive  works  on  the  comparative  anatomy  of  ver- 
tebrates are  Gegenbaur's  Vergleichende  Anatomie  der  Wirbelthiere 
(Engelmann)  and  Owen's  Comparative  Anatomy  and  Physiology 
of  Vertebrates  (Longmans,  Green  &  Co.,  1866). 

The  dogfish  is  described  in  Marshall  and  Hurst's  Practical 
Zoology  (Black),  Parker's  Elementary  Biology  (Macmillan),  and 
Parker  and  Parker's  Practical  Zoology  (Macmillan).  The  skate 
is  described  in  Parker's  Zootomy  (Macmillan).  The  perch  is 
described  in  Vogt  and  Yung's  Vergleichende  Anatomie  (Vieweg). 
In  Parker's  Zootomy  a  description  of  the  cod  is  given.  Necturus 
is  not  described  in  any  text-book.  The  frog  is  described  in  many. 
The  best  descriptive  work  is  Gaupp's  Anatomie  des  Frosches 
(Vieweg).  Extended  descriptions  are  also  found  in  Huxley  and 
Martin's  Practical  Biology  (Macmillan),  Parker  and  Parker's 
Practical  Zoology,  and  Marshall's  Anatomy  of  the  Frog  (Black). 
Extended  descriptions  of  the  turtle  and  the  pigeon  are  found 
in  Martin  and  Moale's  How  to  dissect  a  Chelonian  and  How  to 
dissect  a  Bird  (Macmillan).  A  description  of  the  pigeon  is  also 
found  in  Marshall  and  Hurst's  Practical  Zoology  and  in  Parker's 
Zootomy.  The  cat  is  completely  described  in  Reighard  and  Jen- 
ning's  Anatomy  of  the  Cat  (Holt) ;  less  extended  descriptions  will 
be  found  in  Wilder  and  Gage's  Anatomical  Technology  (Corn- 
stock),  Mivarfs  Cat  (Macmillan),  and  Davison's  Mammalian 
Anatomy  (Blakiston). 

The  best  of  the  larger  general  text-books  of  zoology  are 
Hertwig's  Manual  of  Zoology,  translated  by  Kingsley  (Holt), 
Parker  and  Haswell's  Text-Book  of  Zoology  (Macmillan),  and 
Weysse's  Synoptic  Text-Book  of  Zoology  (Macmillan).  The  por- 
tion of  Hertwig's  Zoology  treating  of  vertebrates  is  especially 
good,  and  gives  a  resume  of  their  comparative  anatomy  and 
classification. 


X  INTRODUCTION 

Classification  of  vertebrates.  The  following  classification  has 
been  taken,  with  some  modifications,  from  Wiedersheim's  Com- 
parative Anatomy. 

I.  Ichthyopsida :  vertebrates  breathing  through  gills  either  a  part  or  all 
of  their  lives. 

A.  Cyclostomata  :  suctorial  fishes,  without  jaws  or  paired  fins. 

1.  Petromyzontidae :  lampreys. 

2.  MyxinoidaB  :  hag  fishes. 

B.  Gnathostomata :  true  jaws  present. 

1.  Pisces :  fishes  with  paired  fins. 

(a)  Elasmobranchii :  cartilaginous  fishes ;  sharks  and  skates. 
(6)  Ganoidei :  sturgeons,  garpikes,  etc. 

(c)  Dipnoi :  lung  fishes. 

(d)  Teleostei  :  bony  fishes ;  the  common  fishes. 

2.  Amphibia :  amphibians  ;  batrachians. 

(a)  Urodela :  tailed  amphibians ;  salamanders. 
(&)  Anura :  tailless  amphibians  ;  frogs  and  toads. 
(c)  Gymnophiona :  limbless  amphibians. 

II.  Sauropsida:   vertebrates   never  breathing   through    gills,   with   one 
occipital  condyle. 

1.  Reptilia :  reptiles. 

(a)  Crocodilia :  crocodiles  and  alligators. 
(6)  Lacertilia :  lizards. 

(c)  Chelonia:  turtles. 

(d)  Ophidia:  snakes. 

2.  Aves :  birds. 

in.  Mammalia  :  vertebrates  which  suckle  their  young. 


YERTEBRATE  ZOOLOGY 

CHAPTER  I 

FISHES 
AN  ELASMOBRANCHIAN  FISH.    THE  DOGFISH 

Several  species  of  dogfish  are  common  along  the  Atlantic 
coast.  They  are  the  smallest  of  the  sharks,  and  feed  upon  other 
fishes,  crustaceans,  mollusks,  and  upon  carrion.  The  species 
which  have  been  used  as  the  basis  of  this  dissection  are  Mustelus 
canis  and  Squalus  acanthias.  The  latter  animal  is  easily  dis- 
tinguished from  the  former  by  the  prominent  spine  which  pro- 
jects from  the  anterior  border  of  each  dorsal  fin. 

For  purposes  of  dissection,  however,  any  species  of  dogfish 
will  do  as  well  as  either  of  these.  The  common  skate  may  also 
be  used;  it  is  a  near  relative  of  the  dogfish,  and  although  in 
external  .form  and  appearance  it  is  very  different  from  that  fish, 
in  internal  structure  it  differs  very  little.  The  main  point  of 
difference  is  the  structure  of  the  pectoral  fins,  which  in  the 
skate  are  enormously  developed  and  are  attached  to  the  side  of 
the  body  along  almost  its  whole  length. 

Three  specimens  will  be  needed  for  a  complete  dissection :  one 
for  the  external  form  and  the  principal  viscera,  including  the 
heart,  the  brain,  and  the  nerves ;  one  for  the  blood  vessels ;  and 
one  for  the  skeleton.  During  the  progress  of  the  dissection  the 
specimens  should  be  kept  in  a  five  per  cent  solution  of  formalin. 

The  body  of  the  dogfish  is  much  elongated  and  nearly  cylin-i 
drical.  The  head  is  dorsoventrally  depressed,  with  a  projecting 
snout  and  a  slitlike  mouth  on  its  ventral  side.  The  hinder  end 
of  the  body  is  laterally  compressed,  and  terminates  with  a  slender 
tail,  which  is  the  principal  organ  of  locomotion. 

1 


2 


VERTEBRATE  ZOOLOGY 


The  entire  body,  including  the  fins  and  the  tail,  is  covered 
with  minute  placoid  scales.  Note  in  which  direction  their  sharp 
points  project.  With  the  aid  of  a  hand  lens  examine  the  scales 
at  different  parts  of  the  body:  they  differ  in  size  at  different 
places,  being  larger  on  the  dorsal  than  on  the  ventral  surface. 
In  the  neighborhood  of  the  mouth  they  have  lost  their  sharp 
points.  Note  that  they  pass  over  the  lips  into  the  mouth  and 
are  continuous  with  the  teeth ;  note  also  that  they  are  arranged 
in  diagonal  rows.  Along  each  side  of  the  body  will  be  seen  the 
lateral  line,  —  a  straight  line  which  extends  the  length  of  the 
body:  it  is  an  organ  of  special  sense. 

Note  the  color  of  the  animal  and  the  variation  of  color  at 
different  parts  of  the  body. 

The  body  of  the  dogfish  may  be  divided  into  three  regions,  — 
the  head,  the  trunk,  and  the  tail.  There  is  no  neck. 

The  head  and  the  trunk.  The  anterior  end  of  the  body  is 
flattened  and  bluntly  pointed.  On  its  lateral  surface  are  the 
elongated  eyes,  each  with  two  lids,  the  lower  one  of  which  can 
be  moved  over  the  eye.  In  Mustelus,  in  addition  to  these,  a 
third  lid,  the  nictitating  membrane,  is  present :  it  is  a  translucent 
membrane  which  can  be  drawn  from  the  inner  corner  of  the  eye 
across  it.  Back  of  the  eyes  on  each  side  are  six  prominent 
openings,  all  of  which  communicate  with  the  pharynx :  these 
are  the  spiracle,  which  is  just  back  of  the  posterior  corner  of  the 
eye,  and  the  five  gill  slits,  just  in  front  of  the  anterior  fins.  The 
spiracle  is  homologous  to  a  gill  slit ;  its  function  is  to  act  as  a 
means  of  ingress  for  the  respiratory  water.  The  gill  slits  con- 
tain the  gills,  —  the  organs  of  respiration.  The  respiratory  water 
passes  into  the  cavity  of  the  mouth  and  pharynx  through  the 
mouth  and  spiracles,  and  out  again  through  the  gill  slits,  bathing 
the  gills  on  its  way. 

Note  the  minute  openings  of  the  mucous  canals  distributed  over 
the  head,  which  appear  as  fine  points  from  which  mucous  can 
be  squeezed :  they  are  sense  organs. 

On  the  under  side  is  the  crescentic  mouth,  armed  with  several 
rows  of  teeth.  In  Mustelus  the  teeth  are  flat  and  platelike ;  in 
Squalus  they  are  sharp.  The  nostrils  are  a  pair  of  irregular 


THE  DOGFISH  3 

openings  in  front  of  the  mouth.  In  the  skate  and  in  some  dog- 
fishes each  nostril  is  connected  with  the  mouth  by  a  groove. 
Probe  the  nostrils  and  determine  that  they  are  blind  sacs  and 
have  no  communication  \vith  the  mouth  cavity.  Distributed 
over  the  ventral  surface  are  the  ventral  mucous  canals. 

The  fins,  or  appendages.  Two  kinds  of  fins  are  present,  —  paired 
fins  and  median  fins.  The  latter  are  the  more  primitive  struc- 
tures and  are  alone  present  in  the  lowest  fishes ;  they  are  simply 
dorsal  and  ventral  flattened  projections  of  the  body.  In  Mustelus 
there  are  two  dorsal  fins,  one  ventral  or  anal  fin,  and  a  heter- 
ocercal  caudal  fin,  the  latter  being  both  dorsal  and  ventral.  In 
Squalus  each  dorsal  fin  is  provided  with  a  sharp  spine,  and  no 
ventral  fin  is  present. 

The  paired  fins  are  horizontal,  flattened  projections  extending 
from  the  latero-ventral  surface  of  the  trunk;  they  are  homol- 
ogous to  the  extremities  of  the  higher  vertebrates.  Two  pairs 
are  present,  —  an  anterior  pair,  the  pectoral  fins,  and  a  posterior 
pair,  the  pelvic  fins;  each  is  supported  by  a  cartilaginous  arch 
within  the  body  wall  called  the  pectoral  girdle  and  the  pelvic  girdle, 
respectively.  They  are  easily  felt  through  the  skin.  In  the 
male  the  pelvic  fins  are  much  longer  than  in  the  female;  the 
inner  border  of  each  is  more  or  less  separated  from  the  remainder 
and  forms  a  long,  rodlike  extension  backwards.  This  is  called 
the  clasper  and  is  of  use  when  the  animals  mate ;  observe  its 
structure. 

The  pelvic  fins  lie  close  together  and  inclose  a  large  median 
opening,  the  anus :  this  is  the  outlet  of  the  cloaca,  a  wide,  shallow 
space  which  receives  the  discharges  of  the  digestive  and  urogen- 
ital  organs.  A  pair  of  small,  slitlike  passages,  called  abdominal 
pores,  one  of  which  is  on  each  side  of  the  cloaca  just  within  its 
lateral  border,  forms  a  means  of  communication  between  the 
abdominal  cavity  and  the  outside;  their  function  is  unknown. 
Probe  them.  Just  in  front  of  these  pores  is  a  conical  median 
projection.  This  is  the  urogenital  papilla  in  the  male,  and  con- 
tains the  outlet  of  the  urogenital  organs,  and  in  the  female  the 
urinary  papilla,  which  contains  only  the  outlet  of  the  kidneys. 
The  genital  opening  in  the  female  is  just  in  front  of  the  papilla. 


4  VERTEBRATE   ZOOLOGY 

At  the  front  end  of  the  cloaca  is  the  opening  of  the  rectum,  the 
hinder  end  of  the  digestive  tract.  The  head  of  the  animal 
extends  back  to  the  first  gill  slit ;  the  anus  forms  the  boundary 
between  the  trunk  and  the  tail. 

Exercise  1.  Draw  a  side  view  of  the  animal  and  label  all  of  the 
various  organs. 

Exercise  2.  Draw  a  dorsal  view  of  the  head,  showing  the  distri- 
bution of  the  mucous  canals. 

Exercise  3.  Draw  a  ventral  view  of  the  head,  showing  the  mucous 
canals  and  the  other  features. 

The  internal  organs.  Determine  the  exact  location  of  the 
pectoral  and  pelvic  girdles,  which  support  the  fins  of  the  same 
name.  Make  an  incision  through  the  body  wall  in  the  mid- 
ventral  line  from  the  pectoral  girdle  to  the  pelvic  girdle ;  then 
continue  the  incision  straight  through  the  pelvic  girdle  to  a 
point  immediately  in  front  of  the  anus,  taking  care  not  to  cut 
too  deeply.  Just  back  of  the  pectoral  girdle  make  a  transverse 
incision  in  each  side  of  the  body  wall ;  make  similar  incisions 
in  front  of  the  pelvic  girdle.  Place  the  animal  on  its  back,  with 
its  head  away  from  you,  on  a  dissecting  board  or  in  a  large  dis- 
secting pan.  Pin  down  the  two  flaps  of  the  body  wall  firmly 
to  the  right  and  left,  and  thus  expose  the  organs  which  lie  in 
the  abdominal  cavity. 

Study  the  position  of  these  organs,  but  without  disturbing 
them.  The  entire  body  cavity  is  divided  by  a  vertical  partition 
into  two  chambers,  —  the  small  pericardial  chamber  at  the  anterior 
end  between  the  gills,  in  which  lies  the  heart,  and  the  large 
abdominal  chamber,  which  contains  the  greater  part  of  the  vis- 
cera ;  the  pericardial  chamber  has  not  yet  been  opened.  These 
cavities  are  lined  by  a  serous  membrane  which  is  called  the 
pericardium  in  the  pericardial  chamber,  and  the  peritoneum  in  the 
abdominal  chamber.  The  partition  separating  these  chambers 
is  situated  just  beneath  the  pectoral  girdle,  and  is  called  the 
false  diaphragm. 


THE   DOGFISH  5 

In  the  forward  part  of  the  abdominal  chamber  is  the  large 
yellowish  or  greenish  liver;  it  is  composed  of  two  principal 
lobes  which  meet  in  front  and  are  attached  to  the  false  dia- 
phragm by  a  mesentery.  Beneath  and  between  the  lobes  of 
the  liver  lie  the  stomach  and  the  intestine.  The  latter  is  a  large 
tube  which  proceeds  directly  back  to  the  cloaca.  The  former 
is  a  bent  V-shaped  tube  in  the  forward  and  middle  portions  of 
the  abdominal  chamber,  which  extends  forward  beneath  (dorsal 
to)  the  liver  to  the  anterior  end  of  the  cavity.  In  Squalus  it  con- 
sists of  two  distinct  portions,  —  a  thick,  straight,  anterior  por- 
tion and  a  V-shaped  portion,  which  are  separated  from  each  other 
by  a  prominent  constriction.  Note  the  membranous  mesentery 
which  unites  the  two  limbs  of  the  stomach.  Attached  to  the 
bend  of  the  stomach  by  a  mesentery,  and  extending  back  of  it, 
is  the  large,  dark-colored  spleen.  At  the  point  where  the  intes- 
tine leaves  the  stomach  will  be  seen  a  portion  of  the  whitish 
pancreas.  Note  the  gall  bladder  imbedded  in  the  liver. 

By  pushing  aside  these  organs,  but  not  cutting  them,  the 
urogenital  organs  will  be  seen  lying  against  the  dorsal  wall 
of  the  body  cavity.  If  the  animal  be  not  yet  adult,  the  genital 
glands  (the  testes  or  the  ovaries)  will  appear  as  a  pair  of  elon- 
gated bodies  of  greater  or  less  size,  but  usually  an  inch  or  two 
in  length,  extending  back  from  the  forward  end  of  the  abdomi- 
nal cavity.  The  dogfish  which  are  bought  for  dissection  are 
usually  immature,  and  the  genital  glands  and  ducts  are  often 
too  small  to  be  studied. 

If  the  animal  be  an  adult  male  (and  the  sex  may  be  deter- 
mined by  the  presence  or  absence  of  the  claspers),  the  testes  will 
appear  as  a  pair  of  elongated,  flattened  bodies,  supported  by 
mesenteries.  If  the  animal  be  an  adult  female,  the  ovaries  will 
be  seen,  —  irregular,  elongated  bodies,  usually  with  yellow 
spherical  ova  projecting  from  the  surface.  The  oviducts  are  a 
pair  of  large  tubes  lying  against  the  dorsal  wall  of  the  abdom- 
inal cavity,  at  the  forward  end  of  which  their  anterior  ends 
fuse  ;  a  single  median  opening  is  present  here  on  the  ventral 
side  of  the  fused  ends,  through  which  the  ova  find  their  way 
into  the  oviducts  from  the  abdominal  cavity.  The  extreme 


6  VERTEBRATE  ZOOLOGY 

posterior  ends  of  the  oviducts  join  each  other  and  open  into  the 
cloaca  by  a  large  pore  just  in  front  of  the  urinary  papilla. 

Exercise  4.  Draw  an  outline  of  the  abdominal  cavity  and  the 
organs  which  appear  in  the  ventral  aspect. 

The  pericardial  cavity  and  the  heart.  The  organs  just  exam- 
ined lie  in  the  abdominal  cavity ;  the  pericardial  cavity  con- 
tains the  heart.  This  organ  in  fishes  stands  in  close  relation  to 
the  gills  and  lies  in  the  mid  ventral  plane  between  them. 

•  Cut  away  the  skin  covering  the  median  portion  of  the  pec- 
toral girdle  and  the  interbranchial  muscles  just  in  front  of  it. 
Cut  away  and  remove  the  girdle  and  the  muscles  and  expose 
the  pericardial  chamber.  Study  the  heart,  which  lies  in  it. 

Note  the  shape  of  the  pericardial  chamber.  Note  also  that  its 
posterior  wall  lies  against  the  anterior  wall  of  the  abdominal  cham- 
ber, and  that  the  two  walls  form  the  false  diaphragm.  The  heart 
consists  of  a  single  ventricle,  which  is  a  muscular  organ  occupying 
a  large  part  of  the  pericardial  chamber ;  a  single  auricle,  which  is 
the  large,  triangular,  thin-walled  sac  lying  dorsal  to  (back  of)  the 
ventricle,  and  appearing  at  its  sides ;  a  conus  arteriosus,  a  muscular, 
cylindrical  prolongation  of  the  anterior  end  of  the  ventricle  ;  and 
the  sinus  venosus,  a  thin-walled  tube  stretching  transversely  across 
the  hinder  part  of  the  pericardial  chamber,  to  the  dorsal  wall  of 
which  it  is  attached.  The  sinus  will  be  seen  by  pressing  the 
ventricle  forward  or  lifting  it  a  little.  Blood  is  brought  from 
the  tissues  and  organs  of  the  body  to  the  sinus  venosus,  from 
which  it  enters  the  auricle.  From  this  vessel  it  is  transferred 
to  the  ventricle,  by  which  it  is  pumped  through  the  conus  arte- 
riosus to  the  gills.  The  heart  contains  only  venous  blood. 

The  pericardial  cavity  is  placed  in  communication  with  the 
abdominal  cavity  by  a  median  canal,  the  pericardio-peritoneal  canal. 
This  is  a  passage  which  opens  into  the  pericardial  cavity  by  a 
large  pore  back  of  the  sinus  venosus,  and  into  the  abdominal 
cavity  back  of  the  ossophagus. 

Exercise  5.  Draw  an  outline  of  the  ventral  aspect  of  the  peri- 
cardial cavity  and  the  organs  in  it. 


THE   DOGFISH  7 

The  inner  structure  of  the  heart.  Cut  open  the  ventricle  and 
conus  arteriosus  by  a  lateral  incision  carried  along  the  left  side 
of  both.  Turn  the  flap,  which  will  constitute  the  entire  ventral 
wall  of  the  heart,  to  one  side,  exposing  its  interior;  wash  this 
out  thoroughly.  The  ventricle  will  be  seen  to  be  a  thick-walled 
vessel  with  a  small  central  cavity  Note  the  muscle  ridges  on 
its  inner  surface.  In  its  dorsal  wall  is  a  large  opening  by  which 
the  auricle  communicates  with  it.  Blow  into  this  auriculo- 
ventricular  opening  with  a  blowpipe. 

Attached  to  the  wall  of  the  conus  arteriosus  are  six  small 
pocketlike  valves  arranged  in  two  rows,  which  permit  the 
blood  to  flow  away  from  the  heart  only.  Bring  them  into 
view  by  means  of  the  blowpipe  ;  note  the  direction  in  which 
they  act. 

Fill  the  auricle  with  air  by  blowing  into  it  through  the 
auriculo-ventricular  opening.  Open  the  auricle  by  a  lateral 
incision  and  wash  it  out.  Note  its  thin  walls  and  its  large 
cavity.  With  the  blowpipe  find  the  opening  into  the  sinus 
venosus. 

Exercise  6.  Draw  a  view  of  the  opened  ventricle  and  conus 
arteriosus,  showing  the  muscle  ridges,  the  valves,  and  the 
openings. 

The  pharynx  and  the  mouth.  Insert  one  blade  of  the  scissors 
in  the  corner  of  the  mouth  on  the  left  side,  and  carry  a  cut 
straight  back  across  the  gills  as  far  as  the  pectoral  girdle. 
From  the  end  of  this  incision  carry  another  across  the  floor  of 
the  pharynx,  just  back  of  the  heart,  to  the  opposite  side  of  the 
body.  Turn  the  flap  thus  formed,  which  is  the  entire  ventral 
side  of  the  head,  over  to  the  animal's  right  and  pin  it  there, 
exposing  the  cavity  of  the  mouth  and  pharynx. 

These  two  cavities  will  be  seen  to  form  a  single  large  space, 
bounded  in  front  by  the  opening  of  the  mouth  and  behind  by 
the  beginning  of  the  gullet  or  oesophagus.  The  whole  is  lined 
by  a  slightly  folded  mucous  membrane.  On  each  side  the  body 
wall  is  pierced  by  six  large  clefts,  of  which  the  five  posterior 
are  the  gill  slits,  and  the  anterior  one  is  the  spiracle.  Probe  these 


8  VERTEBRATE  ZOOLOGY 

clefts.  Examine  the  gills  in  the  gill  slits,  and  the  cartilaginous 
gill  arches  which  support  them.  Note  that  the  hinder  wall  of 
the  last  gill  slit  is  without  a  gill.  The  spiracle  is  homologous 
to  a  gill  slit  and  may  contain  a  rudimentary  gill.  Slit  it  open 
and  examine  its  walls. 

On  the  ventral  side  is  the*  prominent  tongue,  supported  by 
the  hyoid  cartilages  beneath  the  mucous  membrane.  Feel  these 
cartilages  with  the  fingers. 

Observe  the  character  and  arrangement  of  the  teeth  in  both 
upper  and  lower  jaw.  In  Squalus  they  are  sharp,  as  in  the 
majority  of  sharks ;  in  Mustelus  they  have  lost  their  sharp 
points  and  are  reduced  to  flat  plates. 

Exercise  7.  Draw  a  semidiagrammatic  sketch  of  both  dorsal  and 
ventral  walls  of  the  mouth  and  pharynx. 

Cut  two  or  three  gill  arches  from  the  body.  Note  that  each 
gill  is  composed  of  two  rows  of  gill  filaments,  an  anterior  and  a 
posterior  row,  and  that  each  gill  slit  is  bounded  on  the  one  side 
by  the  posterior  filaments  of  one  gill,  and  on  the  opposite  side 
by  the  anterior  filaments  of  the  gill  next  back  of  it.  The  gills 
in  fishes  are  outgrowths  of  the  wall  of  the  pharynx. 

Exercise  8.  Draw  a  gill  slit  and  the  filaments  bounding  it. 

The  digestive  system.  This  system  consists  of  the  mouth, 
pharynx,  oesophagus,  stomach,  intestine,  cloaca,  and  the  three 
intestinal  glands,  —  the  liver,  pancreas,  and  rectal  gland. 

Cut  the  mesentery  which  attaches  the  spleen  to  the  stomach, 
and  remove  the  spleen  from  the  body.  Joining  the  median  por- 
tion of  the  liver  with  the  anterior  end  of  the  intestine  is  a  large 
tubular  vessel,  the  bile  duct,  alongside  which  are  the  hepatic 
artery  and  the  portal  vein;  they  must  not  be  cut.  Note  the 
wide  mesentery  which  joins  the  stomach  and  the  anterior  end 
of  the  intestine  with  the  dorsal  body  wall ;  and  also  the  mesen- 
tery which  joins  the  two  limbs  of  the  V-shaped  stomach. 

Lift  up  the  stomach  and  intestine  and  observe  the  whitish 
pancreas ;  carefully  note  its  shape  and  position.  Find  the  pan- 
creatic duct:  it  is  a  small  tube  which  leaves  the  pancreas  near 


THE   DOGFISH  9 

its  anterior  end  and  enters  the  ventral  wall  of  the  intestine, 
which  it  traverses  a  short  distance. 

Note  that  the  hinder  portion  of  the  intestine  is  not  joined 
with  the  dorsal  body  wall  by  a  mesentery,  except  at  its  extreme 
hinder  end.  Note  the  elongated,  cylindrical  rectal  gland,  which 
lies  in  this  mesentery.  Find  the  duct  which  joins  it  with  the 
rectum. 

Observe  again  the  large  stomach.  The  anterior  end  passes 
forward  beneath  the  liver  and  is  joined  with  the  pharynx  by 
a  very  short  and  equally  thick  oesophagus.  Pass  a  probe  from 
the  pharynx  into  the  stomach.  The  anterior  end  of  the  stomach 
is  called  the  cardiac  end.  The  posterior  V-shaped  portion  of  the 
stomach  is  continuous  with  the  intestine,  the  posterior  end  of 
it  being  called  the  pyloric  end. 

Trace  the  bile  duct  from  the  liver  to  its  point  of  union  with 
the  intestine,  which  is  a  short  distance  posterior  to  the  pylorus. 

The  intestine  is  made  up  of  three  portions,  —  the  duodenum, 
colon,  and  rectum.  The  duodenum  is  very  short  and  forms  the 
anterior  end  of  the  intestine;  it  receives  the  bile  duct.  The 
colon  forms  the  principal  portion  of  the  intestine  and  is  charac- 
terized by  the  presence  in  it  of  an  extensive  spiral  fold  of  the 
mucous  membrane,  called  the  spiral  valve.  This  fold  extends 
from  the  inner  wall  of  the  'intestine  and  almost  fills  it ;  its 
attachment  to  the  intestinal  wall  is  plainly  seen  on  the  outside. 
The  rectum  is  short  and  extends  from  the  colon  to  the  cloaca. 
It  is  joined  by  a  short  duct  from  the  rectal  gland. 

Exercise  9.  Draw  a  semidiagrammatic  sketch  of  the  digestive 
system.  Represent  accurately  the  shape  of  the  liver  and 
the  pancreas,  and  the  bile  and  pancreatic  ducts.  Carefully 
label  all. 

Study  the  spiral  valve.  Make  a  longitudinal  slit  in  the  ventral 
wall  of  the  colon  and  duodenum.  The  spiral  valve  will  be  seen 
to  be  a  wide  fold  which  extends  into  the  cavity  of  the  colon 
from  its  inner  surface,  forming  a  series  of  spirals  nearly  filling 
it.  They  have  the  appearance  of  a  nest  of  elongated  cones,  one 
inside  the  other,  and  opening  backward.  Beginning  at  its  hinder 


10  VERTEBRATE  ZOOLOGY 

end,  cut  the  spiral  valve  from  the  intestinal  wall  with  scissors. 
It  will  be  seen  to  be  a  single  fold. 

The  function  of  the  spiral  valve  is  to  increase  the  intestinal 
surface. 

Exercise  10.  Draw  a  diagram  of  the  spiral  valve. 

Slit  open  the  entire  stomach  and  note  the  folds  in  its  mucous 
membrane. 

The  urogenital  system.  The  urinary  and  the  genital  organs 
are  closely  associated  with  each  other  and  will  be  studied  to- 
gether. Entirely  remove  the  digestive  system  from  the  body. 
In  an  immature  animal  the  genital  organs  cannot  be  studied. 

The  genital  organs  consist  of  the  genital  glands,  which  are  the 
paired  testes  or  ovaries,  and  the  paired  excurrent  canals,  which  in 
the  female  are  the  very  large  oviducts,,  The  testes  or  ovaries, 
as  we  have  already  seen,  are  soft,  elongated  bodies  at  the  for- 
ward end  of  the  abdominal  cavity  and  attached  to  the  dorsal 
body  wall  by  mesenteries.  In  Mustelus  the  two  genital  glands 
are  grown  together. 

The  urinary  organs  are  composed  of  the  paired  kidneys  and  the 
paired  excurrent  canals.  The  kidneys  are  narrow,  elongated  organs 
which  lie,  one  on  each  side  of  the  median  line,  close  against  the 
dorsal  body  wall  and  covered  ventrally  by  the  peritoneum  ;  they 
extend  almost  the  entire  length  of  the  abdominal  cavity.  In 
the  male  the  anterior  half  of  each  kidney  loses  its  excretory 
function  and  enters  into  a  close  relation  with  the  testis. 

The  excurrent  canals  of  the  kidneys  are  called  the  Wolffian 
ducts.  They  differ  considerably  in  the  two  sexes,  in  the  male 
acting  also  as  the  excurrent  ducts  of  the  testes.  The  male 
Wolffian  duct  on  each  side  begins  at  the  forward  end  of  the 
kidney,  appearing  as  a  very  much  convoluted  tube  on  the  ven- 
tral side  of  it,  and  passes  to  tfre  hinder  part  of  the  abdominal 
cavity.  Here  it  joins  the  other  Wolffian  duct,  and  the  median 
vessel  thus  formed  opens  into  the  cloaca  at  the  end  of  the 
urogenital  papilla,  just  behind  the  opening  of  the  rectum. 

The  anterior  and  posterior  portions  of  this  duct  are  very  dis- 
tinct from  each  other.  The  anterior  convoluted  portion,  which 


THE   DOGFISH  11 

is  called  the  epididymis,  is  exclusively  a  sperm  duct,  and  does 
not  carry  urine.  At  its  anterior  end  it  is  connected  by  means 
of  delicate  tubes,  callecj  the  vasa  efferentia,  with  the  anterior  end 
of  the  testis,  from  which  it  receives  sperm.  The  posterior  por- 
tion is  not  convoluted,  and  its  hinder  end  is  enlarged  to  form 
a  seminal  vesicle.  Through  this  portion  the  sperm  is  brought 
from  the  epididymis  to  the  cloaca;  it  also  acts  as  a  ureter,  a 
number  of  urinary  tubes  arising  from  the  kidney  and  proceed- 
ing to  its  hinder  end.  The  Wolffian  duct  thus  acts  both  as  a 
vas  deferens,  or  sperm  duct,  and  as  a  ureter,  and  on  account  of 
this  double  function  is  also  called  the  duct  of  Leydig. 

In  the  female  animal  the  Wolffian  duct  is  exclusively  a 
ureter,  corresponding  to  the  hinder  part  only  of  the  same 
duct  in  the  male,  and  receives  a  number  of  urinary  tubes  from 
different  parts  of  the  kidney.  The  two  Wolffian  ducts  meet 
at  their  hinder  ends,  and  the  median  vessel  thus  formed  opens 
into  the  cloaca  at  the  end  of  the  urinary  papilla,  behind  the 
rectum. 

The  e^current  canals  of  the  genital  organs  in  the  female  are 
called  the  Miillerian  ducts,  or  oviducts ;  they  are  not  present  in  the 
male,  except  sometimes  as  rudiments.  They  are  a  pair  of  large 
tubes  which  extend  the  entire  length  of  the  abdominal  cavity. 
Their  anterior  ends  are  joined,  and  open  into  the  abdominal 
cavity  by  a  large  median  pore  which  is  situated  just  in  front 
of  the  liver  and  beneath  the  oesophagus.  In  the  anterior  part 
of  each  oviduct  is  the  large,  ovoid  shell  gland;  in  its  posterior 
part  is  the  wide,  distended  uterus. 

The  ova  are  thrown  into  the  abdominal  cavity  by  the  rupture 
of  the  walls  of  the  ovaries.  They  pass  into  the  oviducts  through 
the  median  pore  just  mentioned,  where  they  are  fertilized.  They 
remain  in  the  uterus,  in  Squalus  and  Mustelus,  while  develop- 
ment takes  place,  the  young  animals  being  born  alive ;  in  many 
other  sharks  which  are  oviparous  a  characteristic  black,  horny 
shell  is  formed  in  the  uterus. 

Exercise  11.  Make  a  semidiagrammatic  drawing  of  the  urogen- 
ital  system,  so  far  as  observed,  together  with  the  cloaca. 


12  VERTEBRATE  ZOOLOGY 

The  nervous  system.  This  is  made  up  of  three  groups  of 
organs:  (1)  the  central  nervous  system,  which  includes  the  brain 
and  the  spinal  cord;  (2)  the  peripheral  nervous  system,  which 
includes  the  paired  cranial  and  spinal  nerves  by  which  the 
brain  and  the  spinal  cord  are  placed  in  connection  with  the 
various  organs  of  the  body,  and  the  sympathetic  nervous  sys- 
tem whose  function  is  to  innervate  the  important  viscera  of 
the  body  cavity;  and  (3)  the  special  sense  organs,  by  which  the 
animal  is  placed  in  touch  with  its  environment.  We  shall  study 
the  last-named  organs  first. 

The  special  sense  organs  inotude  the  integumental  sense  organs, 
the  olfactory  organs,  the  eyes,  and  the  ears. 

The  integumental  sense  organs.  Imbedded  in  the  skin  of  the 
fish  are  minute  sense  buds  whose  exact  function  is  not  known,  but 
which  undoubtedly  enable  the  animal  to  receive  certain  impres- 
sions from  the  water  surrounding  it.  The  most  important  of  these 
in  the  dogfish  are  the  lateral  line  and  the  ampullae  of  Lorenzini.1 

The  lateral  line  is  a  canal  in  the  integument  which  extends 
along  each  side  of  the  body  from  the  head  to  the  hinder  end ; 
it  appears  on  the  outer  surface  as  a  light-colored  ridge.  In  this 
canal  are  groups  of  sensory  cells  which  are  innervated  by  the 
tenth  cranial  nerve.  Each  of  these  groups  has  a  minute  open- 
ing to  the  outside.  The  lateral  line  also  extends  on  to  the  head, 
but  is  here  difficult  to  see  in  an  ordinary  dissection* 

The  ampullae  of  Lorenzini  are  bulb-shaped  bodies  at  the  end  of 
long  mucous  canals,  which  open  upon  the  head,  and  are  most 
numerous  on  the  snout.  The  external  openings  of  these  canals 
appear  as  dots  upon  the  skin ;  the  canals  are  filled  with  a  trans- 
parent secretion.  The  ampullae  are  collected  in  three  principal 
groups,  the  largest  of  which  is  on  the  under  surface  of  the 
anterior  end  of  the  snout,  while  the  other  two  are  on  the  side 
of  the  head  in  front  of  and  between  the  eyes.  From  these 
points  the  canals  proceed  to  the  external  openings,  which  are 
arranged  in  rows  on  the  head,  and  vary,  consequently,  a  good 
deal  in  length,  some  of  them  measuring  an  inch  or  more. 

1  See  "  The  Function  of  the  Lateral-Line  Organs  in  Fishes,"  by  G.  H.  Parker, 
in  Bulletin  of  Bureau  of  Fisheries  for  1904,  Vol.  XXIV,  p.  183. 


THE  DOGFISH  13 

Observe  the  openings  of  these  canals.  Skin  the  anterior  por- 
tion of  the  head  and  study  the  arrangement  of  the  canals,  tracing 
them  to  their  ends. 

The  olfactory  organ.  Two  nasal  capsules  are  present,  which 
open  to  the  outside  on  the  ventral  surface  of  the  snout,  in  front 
of  the  mouth.  Remove  the  ventral  wall  of  one  of  these  and 
dissect  the  capsule  from  the  body.  Note  its  large  size  and  its 
connection  with  the  olfactory  nerves.  Cut  it  open  and  note  the 
folds  in  its  mucous  membrane,  and. their  arrangement. 

Exercise  12.  Draw  the  nasal  capsule. 

The  eyes.  Cut  away  the  eyelids  of  the  right  eye  and  the 
cartilaginous  ridge  of  the  skull  which  surrounds  it,  so  as  to 
expose  thoroughly  the  orbit.  Study  the  eyeball  as  it  lies  in  the 
orbit.  The  white  pupil,  which  is  an  opening  admitting  light  into 
the  inner  part  of  the  eye,  will  be  seen ;  surrounding  the  pupil 
is  the  black  iris,  and  covering  both  and  forming  the  outer  coat- 
ing of  the  front  of  the  eye  is  the  transparent  cornea.  At  the  back 
and  sides  of  the  eyeball  the  outer  coating  is  called  the  sclera. 
A  transparent  membrane  called  the  conjunctiva,  which  is  contin- 
uous with  the  inner  lining  of  the  eyelid,  passes  over  the  front 
of  the  eye. 

Exercise  13.  Draw  the  front  aspect  of  the  eyeball. 

The  eyeball  is  hemispherical  in  shape,  the  front  surface,  the 
cornea,  being  flattened.  Press  the  eyeball  medially  and  note 
the  broad,  bandlike  nerve  which  lies  across  the  inner  part  of 
the  orbit,  dividing  into  two  branches  near  its  outer  edge. 

The  muscles  of  the  eyeball,  by  means  of  which  its  position 
in  the  socket  can  be  changed,  are  six  in  number.  Press  the 
eyeball  downwards  and  note  on  its  medial  side  two  muscles 
which  are  inserted  close  together.  The  anterior  one  is  the 
superior  oblique  muscle,  which  goes  to  the  inner  anterior  wall  of 
the  orbit;  the  posterior  one  is  the  superior  rectus  muscle,  which 
goes  to  the  inner  posterior  wall  of  the  orbit.  Note  the  white 
nerve  strands ;  they  may  be  distinguished  from  the  muscles  by 
their  whiteness. 


14  VEKTEBKATE   ZOOLOGY 

Press  the  eyeball  backward  and  medially  and  note  the  infe- 
rior oblique  muscle,  which  has  its  insertion  on  the  antero-ventral 
side  of  it  and  goes  to  the  inner  anterior  wall  of  the  orbit.  On 
the  posterior  side  of  the  eyeball  is  the  external  rectus  muscle, 
which  goes  to  the  hinder  wall  of  the  orbit.  Cut  the  superior 
oblique  muscle  at  its  insertion  in  the  eyeball;  beneath  and  in 
front  of  it  will  be  seen  the  internal  rectus  muscle,  which  runs 
back  to  the  hinder  wall  of  the  orbit.  Cut  all  of  these  muscles 
at  their  insertion  on  the  eyeball  and  pull  it  gently  forward;  the 
inferior  rectus  muscle  will  be  seen,  which  passes  from  the  lower 
side  of  the  eyeball  to  the  posterior  wall  of  the  orbit. 

Find  the  optic  nerve  ;  it  will  be  seen  to  enter  the  eyeball. 
Cut  the  nerve  and  remove  the  eyeball  from  the  orbit.  Note 
the  origins  of  the  six  eye  muscles  in  the  orbit;  the  two  oblique 
muscles  will  be  seen  to  take  their  origin  in  its  anterior  wall,  and 
the  four  rectus  muscles  in  its  posterior  wall. 

Study  the  structure  of  the  eyeball.  Its  outer  wall  is  made  up 
of  three  layers,  which  are  called  the  sclera  or  sclerotic  coat,  the 
choroid  coat,  and  the  retina.  The  sclera  is  the  outer  coating;  it 
covers  the  entire  eye  except  in  front,  where  its  place  is  taken 
by  the  cornea. 

Just  within  the  sclera  is  the  choroid  coat.  Cut  the  eyeball  in 
two  by  an  incision  parallel  to  the  cornea,  so  that  you  can  look 
into  the  interior.  The  soft  vitreous  humor  which  forms  the  inner 
portion  of  the  eye  will  exude,  and  the  crystalline  lens  will  be  seen. 
The  choroid  coat  will  be  recognized  by  its  dark  color;  it  con- 
tains the  pigment  of  the  eye  and  the  blood  vessels  which  supply 
it.  On  the  inner  surface  of  the  choroid,  next  to  the  retina,  is  a 
layer  called  the  tapetum  lucidum,  which  reflects  light  and  causes 
the  eye  to  shine  in  the  dark. 

Just  within  the  choroid  and  forming  the  inner  lining  of  the 
eye  is  the  retina ;  it  is  light  in  color  and  is  easily  separated  from 
the  choroid. 

The  retina  represents  an  expansion  of  the  optic  nerve  on  the 
inner  surface  of  the  eye,  and  is  the  portion  of  it  which  is  sensi- 
tive to  light.  Note  the  point  where  the  optic  nerve  pierces  the 
sclera  and  choroid ;  this  point  is  called  the  blind  spot  because  it 


THE  DOGFISH  15 

is  nonsensitive.  Projecting  from  the  inner  surface  of  the  eye 
very  near  the  blind  spot  is  a  slender  rod  called  the  processus  falci- 
formis;  it  ends  in  an  enlargement  called  the  campanula  Halleri, 
which  rests  against  the  lens.  The  campanula  is  composed  mainly 
of  smooth  muscle  fibers  by  the  action  of  which  the  position  of 
the  lens  is  slightly  changed  and  a  certain  degree  of  accommo- 
dation is  effected.  A  ciliary  apparatus,  which  is  the  principal 
organ  of  accommodation  in  the  eyes  of  the  higher  vertebrates, 
is  not  present. 

The  eye  has  in  it  two  principal  chambers,  —  an  anterior  cham- 
ber between  the  iris  and  the  cornea,  which  is  filled  with  a  watery 
fluid  called  the  aqueous  humor,  and  a  large  posterior  chamber 
which  is  filled  with  the  gelatinous  vitreous  humor. 

Exercise  14.  Draw  a  diagram  showing  the  position  of  the  muscles 
of  the  eyeball. 

Exercise  15.  Draw  a  diagram  showing  the  structure  of  the  eye. 

The  ear.  An  internal  ear  is  alone  present  in  fishes,  there  being 
no  outer  ear  and  no  ear  opening.  The  internal  ear  is  a  mem- 
branous labyrinth,  which  is  inclosed  in  a  cartilaginous  capsule 
situated  immediately  back  of  the  posterior  margin  of  the  orbit  on 
each  side.  It  is  made  up  of  a  spherical  sac,  the  vestibule,  from 
the  dorsal  surface  of 'which  spring  three  semicircular  canals,  —  an 
anterior  vertical,  a  posterior  vertical,  and  a  horizontal  canal.  Each 
of  these  canals  has  a  small  swelling  at  one  end  called  an  ampulla. 
From  the  dorsal  surface  of  the  vestibule  there  also  arises  a  deli- 
cate tube,  the  endolymphatic  duct,  which  passes  through  the  roof 
of  the  skull  to  the  outer  skin,  which  is  here  pierced  by  a  small 
hole.  The  ear  comes  into  existence  in  the  embryo  as  an  infold- 
ing of  the  outer  wall  of  the  head,  and  this  duct  is  a  remnant  of 
this  infolding. 

The  membranous  labyrinth  is  extremely  delicate  and  is  diffi- 
cult to  dissect.  With  care  and  patience,  however,  this  may 
be  done ;  the  semicircular  canals,  at  least,  should  be  found. 
Remove  the  skin  and  muscles  completely  from  the  top  of  the 


16  VEETEBEATE  ZOOLOGY 

head  back  of  the  eye  on  the  right  side.  A  ridge  will  be  seen  in 
the  roof  of  the  skull  extending  backward  from  the  orbit.  Within 
this  ridge  and  immediately  beneath  its  cartilaginous  wall  is  the 
anterior  vertical  semicircular  canal.  Very  carefully  shave  off 
the  roof  of  the  ridge  and  find  it;  it  will  be  seen  to  have  the 
diameter  of  a  fine  needle.  Just  back  of  it  is  the  posterior  verti- 
cal canal.  Lying  between  the  hinder  end  of  this  canal  and  the 
orbit  in  the  cartilage  is  the  horizontal  canal.  Note  the  ampulla 
of  each  of  these  canals.  Beneath  them  is  the  vestibule. 

In  most  fishes  the  ear  has  no  auditory  function,  but  is  an 
organ  of  equilibrium. 

Exercise  16.  Draw  the  membranous  labyrinth  so  far  as  observed. 

The  central  nervous  system.  Remove  the  skin  and  muscles 
from  the  dorsal  surface  of  the  head.  Very  carefully  shave  off 
the  roof  of  the  skull  and  expose  the  dorsal  surface  of  the  brain ; 
do  not  disturb,  however,  any  part  of  the  orbits  of  the  eyes  or  the 
nerves  in  them. 

The  brain,  as  it  appears  in  a  dorsal  view,  is  made  up  of  five 
divisions, — the  cerebrum,  thalamencephalon,  optic  lobes,  cerebel- 
lum, and  medulla  oblongata,  of  which  the  cerebrum  and  cerebel- 
lum are  much  more  prominent  than  the  other  three  divisions. 
The  cerebrum  is  the  anterior  division  and  is  composed  of  a  pair 
of  rather  indistinctly  marked  hemispheres,  from  each  of  which  a 
large  olfactory  lobe  projects  forward  to  the  nasal  capsule. 

The  second  division,  the  thalamencephalon,  is  a  small  area  just 
back  of  the  cerebrum.  Its  dorsal  wall  is  thin  and  supports  the 
pineal  body,  a  very  slender  projection  which  extends  forward  and 
dorsally  to  the  skull ;  it  may  have  been  removed  with  it.  The 
third  division,  the  optic  lobes  or  midbrain,  consists  of  a  pair  of 
rounded  bodies  back  of  the  thalamencephalon.  The  fourth  divi- 
sion is  the  cerebellum,  a  prominent,  elongated  body  which  extends 
forward  over  the  posterior  portion  of  the  optic  lobes  and  back- 
ward over  the  fifth  division;  it  is  divided  into  several  lobes. 
The  fifth  division  is  the  medulla  oblongata ;  it  forms  the  hinder 
portion  of  the  brain  and  is  continuous  with  the  spinal  cord ;  in 
its  delicate  dorsal  wall  is  a  large  depression  called  the  fossa 


THE  DOGFISH  17 

rhomboidalis,  at  the  sides  of  which  is  a  pair  of  lateral  projections, 
the  restiform  bodies. 

Exercise  17.  Draw  the  dorsal  aspect  of  the  brain  on  a  scale  of 
2  or  3 ;  carefully  label  its  parts. 

The  cranial  nerves.    Ten  pairs  of  these  nerves  are  present, 
which,  with  their  most  important  branches,  are  the  following : 

1.  The  olfactory  nerves.    These  nerves  form  a  large  group  of 
minute  fibers  which  extend  from  the   anterior   end   of   each 
olfactory  lobe  into  the  nasal  capsules.     Look  for  them  on  the 
right  side  of  the  head ;  they  will  be  seen  by  pressing  the  ante- 
rior end  of  the  olfactory  lobe  back  from  the  wall  of  the  nasal 
capsule. 

2.  The  optic  nerves  arise  on  the  ventral  surface  of  the  thala- 
mencephalon,  where  they  will  be  seen  when  the  ventral  surface 
of  the  brain  is  studied ;   each  passes  through  a  foramen  in  the 
orbit  to  the  eye.    Press  the  side  of  the  skull  gently  from  the 
brain  and  find  them. 

3.  The  oculomotor  is  a  small  nerve  which  arises  in  the  ventral 
surface  of  the  optic  lobe  on  each  side  and  passes  laterally  to  the 
orbit;  it  enters  the  orbit  a  short  distance  back  of  the  optic 
nerve  and  goes  to  the  inferior  rec^tus,  the  superior  rectus,  and 
the  inferior  oblique  muscles.    It  may  be  seen  by  pressing  the 
side  of  the  skull  away  from  the  optic  lobes. 

4.  The  trochlear  or  pathetic  nerve  is  a  delicate  strand  which 
arises  from  the  latero-dorsal  surface  of  the  brain  between  the 
optic  lobe  and  the  cerebellum.    It  runs  forward  to  the  orbit, 
which  it  enters  above  the  optic  nerve,  and  goes  to  the  superior 
oblique  muscle.    It  may  be  seen  emerging  from  beneath  the  ante- 
rior portion  of  the  cerebellum  and  passing  to  the  orbit. 

5.  The  trigeminal  nerve  arises  from  the  side  of  the  anterior  end 
of  the  medulla  in  close  connection  with  the  seventh  and  eighth 
nerves  and  opposite  the  posterior  portion  of  the  cerebellum. 
Cut  away  the  wall  of  the  skull  and  find  these  three  nerves. 
The  trigeminal  nerve  has  three  main  branches.    (1)  The  ophthal- 
mic branch  leaves  it  almost  at  its  origin  and  enters  the  orbit, 
along  the  medial  side  of  which  it  passes  to  its  anterior  end; 


18  VERTEBRATE  ZOOLOGY 

here  it  passes  out  through  a  foramen  and  runs  forward  on  the 
dorsal  surface  of  the  snout,  where  it  innervates  the  Lorenzinian 
ampullae.  (2)  The  maxillary  branch  and  (3)  the  mandibular  branch 
form  the  main  part  of  the  trigeminal,  which  enters  the  orbit  as 
one  nerve  by  a  foramen  at  its  hinder  end  and  runs  diagonally 
across  the  floor  of  the  orbit  as  a  broad  band  to  its  outer  margin, 
where  it  divides  into  these  two  branches.  They  at  once  emerge 
from  the  orbit  and  go  to  the  Lorenzinian  ampullae.  Trace  them 
as  far  as  possible. 

6.  The  abducens  is  a  very  small  nerve  which  arises  from  the 
ventral  surface  of  the  medulla  near  the  median  line  behind  the 
roots  of  the  trigeminal,  and  passes  through  the  same  foramen 
with  this  nerve  into  the  orbit  to  the  external  rectus  muscle.    The 
root  of  this  nerve  will  be  seen  when  the  ventral  surface  of  the 
brain  is  studied. 

7.  The  facial  nerve  arises  in  connection  with  the  trigeminus. 
It  sends  out  three  main  branches.   (1 )  The  ophthalmic  branch  passes, 
together  with  the  ophthalmic  branch  of  the  trigeminal  nerve, 
along  the  medial  wall  of  the  orbit  to  the  ampullae  of  Lorenzini 
on  the  snout.    (2)  The  palatine  branch  and  (3)  the  hyoid  branch  form 
the  main  part  of  the  facial,  which  enters  the  orbit  as  a  single 
nerve  directly  back  of  the  trigeminal,  and  divides  into  these  two 
branches.    The  palatine  passes  across  the  floor  of  the  orbit  par- 
allel with  the  large  trigeminal  nerve  branch ;  the  hyoid  branch 
runs  across  the  posterior  part  of  the  orbit  to  the  spiracle  and  the 
hyoid  arch. 

8.  The  auditory  nerve  is  a  large,  short  nerve  which  arises  in 
connection  with  the  trigeminal  and  facial  nerves  and  almost  at 
once  enters  the  auditory  capsule.    It  is  the  shortest  cranial  nerve 
and  the  only  one  which  remains  within  the  cranium.    It  may  be 
seen  by  pressing  the  wall  of  the  skull  away  from  the  brain. 

9.  The  glossopharyngeal  nerve  arises  on  the  side  of  the  medulla 
some  distance  back  of  the  auditory  nerve.    It  may  be  seen  by 
pressing  the  wall  of  the  skull  away  from  the  brain.    It  a"t  once 
enters  a  foramen  in  the  inner  wall  of  the  auditory  capsule  and, 
passing  through  the  capsule,  divides  into  two  branches  which 
go  to  the  hyoid  arch  and  the  first  gill  arch. 


THE  DOGFISH  19 

10.  The  vagus,  or  pneumogastric,  is  a  large  nerve  which  arises 
by  a  number  of  roots  on  the  side  of  the  medulla  near  its  dorsal 
surface.  It  passes  out  of  the  skull  at  once  by  a  foramen  back 
of  the  auditory  capsule  and  runs  back,  as  a  broad  band,  along 
the  inner  side  of  the  gill  arches,  sending  a  large  branch  to  each 
of  the  hinder  four  arches.  It  also  gives  off,  in  front  of  these 
gill  nerves,  the  lateral-line  nerve,  which  passes  to  the  lateral  line 
and  runs  parallel  to  it  to  the  hinder  end  of  the  body.  The  main 
portion  of  the  vagus,  after  giving  off  the  gill  nerves,  supplies 
the  heart,  stomach,  and  other  organs. 

Exercise  18.  Draw  a  side  view  of  the  brain,  showing  the  cranial 
nerves,  so  far  as  they  have  been  observed. 

The  ventral  surface  of  the  brain.  Remove  the  two  sides  of 
the  skull.  Separate  both  olfactory  lobes  from  their  capsules  and 
bend  the  cerebrum  back,  exposing  its  ventral  surface.  Press 
the  side  of  the  brain  away  from  the  under  portion  of  the  skull 
and  note  the  small  trochlear  nerve  which  issues  from  the  ventral 
surface  of  the  optic  lobe  and  enters  the  orbit,  and  also  the  small 
abducens  nerve  which  issues  from  the  medulla  and  also  goes  to 
the  orbit.  Cut  these  nerves.  Cut  the  optic  nerves  and  note  back 
of  them  a  pair  of  lobed  bodies,  the  lobi  inferiores,  between  which 
is  a  median  projection,  the  infundibulum.  Extending  backward 
from  the  infundibulum  is  the  hypophysis,  or  pituitary  body,  which 
fills  a  deep  depression  in  the  ventral  wall  of  the  skull.  All  of 
these  structures  belong  to  the  thalamencephalon.  Back  of  the 
infundibulum  the  ventral  surface  of  the  brain  is  without  impor- 
tant special  structures. 

Exercise  19.  After  removing  the  brain  from  the  body,  draw  the 
ventral  aspect  on  a  scale  of  2  or  3,  and  carefully  label  all 
the  organs  observed. 

The  ventricles  of  the  brain.  The  brain  is  a  hollow  structure 
and  contains  a  series  of  spaces  which  are  continuous  with  the 
central  canal  of  the  spinal  cord.  In  the  two  hemispheres  are 
two  large  spaces  called  the  first  and  second,  or  the  lateral,  ventricles. 
Make  a  transverse  incision  across  the  hemispheres  and  observe 


20  VERTEBRATE  ZOOLOGY 

them.  In  the  thalamencephalon  is  the  third  ventricle,  which  joins 
the  first  two  at  its  forward  end.  The  roof  of  the  third  ventricle 
is  the  thin  dorsal  wall  of  the  thalamencephalon,  which  has  been 
already  mentioned.  The  fourth  ventricle  is  in  the  medulla,  where 
it  occupies  the  fossa  rhomboidalis,  the  roof  of  which  is  also  very 
thin.  The  third  and  fourth  ventricles  are  joined  by  a  canal 
called  the  aqueductus  Sylvii ;  this  canal  passes  between  the  optic 
lobes  and  communicates  with  the  large  space  in  each  of  them. 
Bisect  the  brain  and  observe  these  spaces. 

Exercise  20.  Draw  a  diagram  representing  the  cavities  of  the 
brain. 

The  vascular  system.  This  system  consists  of  the  following 
organs :  (1)  the  heart,  the  muscular  pump  which  sends  venous 
blood  to  the  gills  to  be  purified;  (2)  the  arterial  system,  which 
carries  (a)  venous  blood  from  the  heart  to  the  gills,  and  (b) 
arterial  blood  from  the  gills  to  the  tissues  ;  (3)  the  venous  system, 
which  includes  (a)  the  systemic  veins,  which  carry  blood  directly 
to  the  heart,  and  (b)  the  portal  veins,  which  carry  blood  directly 
to  the  liver  and  the  kidneys,  from  which  organs  it  passes  to  the 
heart ;  (4)  the  capillaries,  the  minute  vessels  by  which  the  blood 
is  distributed  in  the  tissues. 

We  shall  first  study  the  portal  veins.  Two  systems  of  these 
veins  are  present,  —  (1)  the  hepatic  portal  system,  which  carries 
blood  from  the  digestive  tract  and  spleen  to  the  liver,  and  (2) 
the  renal  portal  system,  which  carries  blood  from  the  hinder 
portions  of  the  body  to  the  kidneys. 

The  hepatic  portal  system.  Place  the  animal  on  its  back  with 
its  head  away  from  you,  and  open  the  abdominal  cavity  in  the 
manner  already  described  (see  page  4).  A  large  vein  will  be 
seen  passing  from  the  anterior  end  of  the  intestine  to  the  liver; 
and  entering  it  near  the  median  plane ;  this  is  the  hepatic  portal 
vein.  Trace  it  forward  into  the  liver,  on  the  dorsal  surface  of 
which  it  will  be  seen  to  break  up  into  several  branches,  which 
go  to  the  different  lobes  of  that  organ. 

Trace  the  vein  backward;  it  will  be  seen  to  be  formed  by 
the  union  of  several  large  veins  from  the  intestine,  stomach, 


THE  DOGFISH  21 

pancreas,  and  spleen.1    Cut  the  mesentery,  where  necessary,  and 
determine  the  course  of  these  veins  and  their  branches. 

Exercise  21.  Draw  a  diagram  representing  the  hepatic  portal 
system,  including  outlines  of  the  liver,  stomach,  intestine, 
pancreas,  and  spleen. 

The  renal  portal  system  consists  of  the  caudal  vein  and  two 
renal  portal  veins.  The  former  lies  in  the  median  line  in  the  tail 
immediately  below  the  spinal  column;  it  and  the  dorsal  aorta, 
which  lies  just  above  it,  are  inclosed  in  the  cartilaginous  arches 
of  the  ventral  side  of  the  vertebrae.  The  caudal  vein  enters  the 
*  abdominal  cavity  at  its  hinder  end  and  at  once  divides  into  a 
right  and  a  left  renal  vein,  each  of  which  passes  to  the  lateral 
side  of  a  kidney  and  sends  numerous  branches  into  it  along  its 
entire  length. 

Exercise  22.  Draw  a  diagram  of  the  renal  portal  system. 

The  systemic  veins,  which  form  the  main  venous  system,  are 
characterized  by  their  great  size,  being  in  some  places  so  wide 
that  they  are  called  sinuses.  These  veins  include  a  pair  of  ante- 
rior and  a  pair  of  posterior  cardinal  sinuses,  which  bring  blood  from 
the  anterior  and  posterior  parts  of  the  body  respectively.  The 
anterior  and  posterior  cardinals  on  each  side  meet  in  a  common 
transverse  sinus  called  the  duct  of  Cuvier,  which  extends  from  the 
end  of  the  sinus  venosus  dorsally  and  laterally.  Opening  into 
the  sinus  venosus,  also,  near  the  median  plane  is  a  pair  of 
hepatic  sinuses,  which  bring  blood  from  the  liver.  The  cardinal 
vessels  are  dorsal  in  position  and  the  hepatic  sinuses  are  ventral. 

Entering  the  anterior  end  of  the  posterior  cardinal  sinus  from 
behind,  on  each  side,  are  the  lateral  vein  and  the  subclavian  vein. 
The  former  will  be  seen  extending  along  the  inner  surface  of 
the  wall  of  the  abdominal  cavity  from  one  end  of  it  to  the  other, 
opposite  the  lateral  line;  the  latter  lies  along  the  pectoral 
girdle  and  brings  blood  from  the  pectoral  fin.  The  iliac  vein, 

1  If  the  hepatic  portal  vein  be  injected,  these  veins  will  be  made  more  promi- 
nent. They  are,  however,  usually  easy  to  study  without  injection,  because  they 
usually  contain  blood,  which  colors  them. 


22  VEETEBEATE  ZOOLOGY 

which  brings  blood  from  the  pelvic  fin,  enters  the  lateral  vein. 
Find  these  veins.1 

Cut  away  enough  of  the  pectoral  girdle  and  ventral  body  wall 
to  give  free  access  to  the  interior  of  the  pericardial  cavity; 
note  the  sinus  venosus  as  it  stretches  across  the  hinder  end  of 
the  cavity,  to  the  dorsal  wall  of  which  it  is  attached.  Slit  open 
the  sinus  venosus,  exposing  its  inner  surface,  and  wash  it  out  if 
necessary.  Note  its  extension  at  each  side  in  a  dorsal  direction 
to  form  the  duct  of  Cuvier ;  probe  this  duct. 

Cut  across  the  main  lobes  of  the  liver  and  near  the  center 
of  each  find  the  large  hepatic  sinus.  Follow  each  sinus  forward, 
slitting  it  open ;  at  its  forward  end  find,  by  means  of  the  probe, 
its  opening  into  the  sinus  venosus.  Note  the  small  veins  which 
are  tributary  to  the  hepatic  sinus. 

Find  the  posterior  cardinal  sinuses,  then  the  lateral  vein  and 
the  subclavian  vein.  The  posterior  cardinals  extend  along  the 
entire  length  of  the  dorsal  wall  of  the  abdominal  cavity.  Their 
anterior  ends  communicate  with  each  other;  —  they  are  a  pair  of 
very  wide  sacs  just  behind  the  false  diaphragm  and  against  the 
dorsal  body  wall.  Posteriorly  the  sinuses  are  narrow,  being  long, 
slender  vessels  close  to  the  median  line  and  separated  from  each 
other  only  by  the  median  vertical  mesentery.  Note  the  numer- 
ous small  renal  veins  which  enter  them  from  the  kidneys. 

Slit  open  the  right  duct  of  Cuvier  and  wash  it  out  if  neces- 
sary ;  cut  open  the  saclike  anterior  end  of  the  posterior  cardinal 
and  trace  it  backwards. 

Study  the  anterior  cardinal  sinuses  which  pass  forward  from 
the  ends  of  the  ducts  of  Cuvier.  In  order  to  find  the  anterior 
cardinal  on  the  right  side,  turn  the  animal  over  so  that  its  dor- 
sal side  is  uppermost,  and  make  a  short,  deep,  longitudinal  inci- 
sion about  halfway  between  the  middorsal  line  and  the  foremost 
gill  slits.  The  anterior  cardinal  sinus  lies  just  above  the  gill 
arches  and  will  be  reached  by  the  incision.  Probe  the  sinus 
back  to  the  duct  of  Cuvier  and  slit  it  open.  Follow  it  forward 

1  These  veins  and  sinuses  can  usually  be  studied  without  injection,  because 
they  are  colored  by  the  blood  in  them.  If  it  is  wished  to  inject  them,  it  may  be 
done  through  the  lateral  vein. 


THE  DOGFISH  23 

to  the  eye,  where  it  opens  into  the  orbital  sinus  which  surrounds 
the  eyeball. 

Exercise  23.  Draw  a  diagram  of  the  systemic  veins,  so  far  as 
observed. 

The  arterial  system.  The  principal  vessels  which  form  this 
system  are  the  following :  (1)  the  ventral  aorta,  or  aorta  ascendens, 
which  passes  forward  from  the  conus  arteriosus ;  (2)  the  afferent 
branchial  arteries,  which  branch  off  from  this  aorta  and  carry 
venous  blood  to  the  gills ;  (3)  the  efferent  branchial  arteries,  which 
collect  the  arterial  blood  from  the  gills  and  carry  it  dorsally  to 
the  middorsal  line  of  the  body  cavity,  where  they  form  (4)  the 
dorsal  aorta,  or  aorta  descendens,  a  median  vessel  which  takes  the 
blood  to  the  hinder  part  of  the  abdominal  cavity.1 

Follow  the  ventral  aorta  from  the  conus  arteriosus  forward, 
cutting  away  the  skin  and  muscles  between  the  gill  arches. 
Three  afferent  arteries  will  be  seen  to  branch  off  on  each  side, 
the  anterior  and  posterior  ones  of  which  divide  each  into  two 
arteries.  Follow  these  five  arteries  between  the  gill  slits  and 
study  their  relation  to  them. 

Exercise  24.  Make  a  semidiagrammatic  drawing  of  the  ventral 
aorta  and  the  afferent  arteries,  showing  their  relation  to 
the  gill  slits  and  arches. 

We  shall  now  study  the  efferent  branchial  arteries,  the  dorsal 
aorta,  and  their  branches.  Insert  one  blade  of  the  scissors  in 
the  left  corner  of  the  mouth  and  carry  an  incision  straight  back 
across  the  gills  as  far  as  the  pectoral  girdle.  From  the  end  of 
this  incision  carry  another  across  the  floor  of  the  pharynx  to  the 
opposite  side  of  the  body.  Turn  the  flap  thus  formed,  which 
is  the  entire  ventral  part  of  the  head,  over  to  the  animal's  right 
and  pin  it  there,  exposing  the  cavity  of  the  mouth  and  pharynx. 

1  The  ventral  aorta  and  the  afferent  branchial  arteries  should  be  injected 
through  the  conus  arteriosus.  The  rest  of  the  arterial  system  may  be  injected 
through  the  caudal  artery,  which  is  the  continuation  in  the  tail  of  the  dorsal 
aorta.  Cut  off  the  tail  a  short  distance  back  of  the  anus  and  insert  the  canula 
in  this  artery. 


24  VEETEBEATE  ZOOLOGY 

Remove  the  mucous  membrane  from  the  roof  of  the  mouth 
and  pharynx  and  from  the  gill  arches,  being  careful  not  to  injure 
the  blood  vessels  just  beneath  it.  The  cartilages  forming  the 
skull  and  gill  arches  will  now  come  into  view.  Four  prominent 
efferent  arteries  will  be  seen  converging  towards  the  median  line, 
each  one  lying  along  the  anterior  border  of  a  cartilage.  Trace 
each  artery  forward  to  its  gill  slit  and  observe  its  two  branches, 
one  of  which  lies  along  each  side  of  the  slit,  anastomosing  at  its 
lower  end.  The  fifth  gill  slit,  which  has  but  a  single  gill,  receives 
a  branch  of  the  fourth  artery.  Observe  carefully  the  short  arteries 
which  connect  the  anterior  branch  of  one  efferent  artery  with 
the  posterior  branch  of  the  one  just  in  front  of  it. 

Find  and  trace  the  branch  of  the  fourth  efferent  artery  which V 
passes  ventrally  to  the  pericardial  cavity  and  supplies  it  and  the 
heart  with  blood ;  also  the  branches  of  the  first  efferent  artery 
which  go  forward  and  supply  the  head. 

The  efferent  arteries  meet  in  the  median  plane  and  form  the 
dorsal  aorta.  Issuing  from  the  aorta  between  the  third  and 
fourth  efferent  arteries  is  a  pair  of  subclavian  arteries.  One  of 
these  extends  to  the  pectoral  fin  on  each  side  and  also  gives  rise 
to  the  lateral  artery,  which  extends  along  the  side  of  the  body 
beneath  the  lateral  line. 

Exercise  25.  Draw  a  diagrammatic  sketch  of  the  efferent  bran- 
chial arteries  and  their  branches. 

The  dorsal  aorta  is  a  large  median  artery  which  lies  just  beneath 
the  spinal  column  in  the  body  cavity  ;  back  of  the  anus  it 
becomes  the  caudal  artery,  which  lies  in  the  ventral  arches  of 
the  vertebral  column.  It  gives  off  the  following  arteries:  the 
spinal  arteries,  small  paired  vessels  arising  at  regular  intervals 
and  going  to  the  muscles  of  the  body  wall ;  the  coaliac  artery,  a 
large  median  vessel  which  arises  from  the  aorta  near  its  anterior 
end  and  passes  backward  to  the  V-shaped  portion  of  the  stomach, 
where  it  sends  branches  to  the  stomach,  liver,  intestines,  pan- 
creas, and  spleen ;  the  anterior  mesenteric  artery,  a  median  vessel 
which  sends  branches  to  the  spleen  and  the  spiral  valve ;  the 
posterior  mesenteric  artery,  which  arises  from  the  aorta  near  its 


THE  DOGFISH  25 

hinder  end  and  passes  to  the  rectal  gland  ;  the  renal  arteries,  small 
paired  arteries  which  leave  the  aorta  at  intervals  along  its  course 
and  go  to  the  dorsal  surface  of  the  kidneys ;  the  iliac  arteries,  a 
pair  of  small  paired  arteries  which  go  to  the  pelvic  fins. 

Exercise  26.  Draw  a  diagrammatic  sketch  of  the  dorsal  aorta  and 
its  branches. 

Exercise  27.  Draw  a  diagram  of  the  entire  vascular  system. 
•f? 

The  body  muscles.  Remove  the  skin  from  a  part  of  the  body 

in  the  caudal  region  and  study  the  muscles  which  form  the  sides 
of  the  body.  On  each  side  a  series  of  muscle  segments  is  present 
called  myotomes  or  myomeres,  which  are  separated  from  one  another 
by  connective-tissue  septa  called  myocommas.  Each  myotome 
forms  an  irregular  plate  and  is  composed  of  parallel  muscle 
fibers  which  will  be  seen  running  across  from  one  myocomma 
to  the  other.  The  fibers  are  thus  not  bound  together  by  fasciae 
into  distinct  muscles,  as  is  the  case  in  the  higher  vertebrates. 
Note  the  zigzag  shape  of  the  outer  edge  of  the  myotome  between 
the  dorsal  and  the  ventral  sides  of  the  body. 

Exercise  28.  Make  an  outline  drawing  of  the  side  of  the  body, 
showing  a  few  of  the  myotomes  with  their  fibers,  and  the 
myocommas. 

Cut  the  tail  off  a  short  distance  behind  the  anus  and  examine 
the  cut  surface.  The  myotomes  appear  here  in  groups  of  con- 
centric circles.  This  appearance  is  partly  due  to  the  zigzag 
shape  of  the  myotomes.  Cut  horizontal  and  dorsoventral  sec- 
tions of  the  muscles  and  determine  the  exact  shape  and  arrange- 
ment of  the  myotomes. 

Observe  the  other  structures  in  the  cross  section.  In  the 
center  of  it  is  the  spinal  column.  The  neural  arch,  within  which 
is  the  spinal  cord,  forms  its  dorsal  portion,  and  the  haemal  arch, 
containing  the  caudal  artery  and  the  caudal  vein,  form  its  ven- 
tral portion  ;  the  vein  is  beneath  the  artery. 

Exercise  29.  Draw  the  cross  section  and  label  all  of  these 
features. 


26  VEKTEBKATE  ZOOLOGY 

The  skeletal  system.  The  skeleton  of  the  dogfish  is  made  up 
of  two  distinct  parts,  the  exoskeleton  and  the  endoskeleton.  The 
former  is  of  integumental  origin  and  consists  of  the  placoid  scales, 
the  teeth,  and  the  delicate  horny  rods  in  the  fins.  Each  placoid 
scale  consists  of  a  basal  plate  of  bone,  which  is  sunk  in  the  der- 
mis  of  the  skin,  and  a  flattened  toothlike  spine,  which  projects 
backward  through  the  epidermis.  The  basal  plates  are  set  close 
together  so  that  the  entire  body  of  the  animal,  including  the 
fins,  is  covered  with  a  coat  of  mail  of  bone.  The  scales  pass  over 
the  lips  into  the  mouth  and  are  continuous  with  the  teeth,  which 
have  essentially  the  same  structure  as  the  spines  of  placoid  scales. 

Placoid  scales  have  furnished  the  beginnings  not  only  of 
teeth  throughout  the  group  of  vertebrates  but  also  of  certain  of 
the  bones  of  the  skull.  Dogfish  and  their  allies  have  no  bony 
skull,  but  in  the  higher  fishes  and  the  higher  vertebrates  gen- 
erally those  bones  called  membrane  bones,  whose  place  in  the 
skull  was  not  taken  by  cartilage  before  the  skull  became  a  bony 
structure,  but  by  membranes  or  portions  of  the  integument,  came 
into  existence  in  the  first  place  by  the  fusion  of  the  bony  plates 
of  placoid  scales. 

Boil  a  piece  of  the  skin  in  caustic  potash  and  isolate  the 
scales.  Mount  some  of  them  in  water  and  study  them  under 
the  microscope. 

Exercise  30.  Make  a  drawing  of  several  scales. 

Exercise  31.  Isolate  several  teeth  and  make  a  drawing  of  them. 

The  endoskeleton  of  the  dogfish  is  the  inner  framework  of  the 
body.  It  is  composed  entirely  of  cartilage,  which  in  certain 
places,  as  the  vertebrae,  is  hardened  by  the  presence  of  carbonate 
of  lime.  The  race  of  sharks  is  an  extremely  ancient  one,  having 
been  already  in  existence  at  the  time  in  the  world's  history 
when  cartilage  and  not  bone  was  the  principal  constituent  of 
the  vertebrate  skeleton.  It  has  remained  in  this  primitive  con- 
dition down  to  the  present  time,  although  in  all  the  higher 
fishes  and  in  other  vertebrates  cartilage  has  given  place  to  bone 
as  the  principal  substance  of  which  the  skeleton  is  formed. 


THE  DOGFISH  27 

Notwithstanding  this  fact  the  sharks  are  at  the  present  time, 
and  probably  have  never  ceased  to  be,  the  largest  and  most 
powerful  fishes  in  the  sea. 

The  endoskeleton  may  be  divided  into  the  axial  skeleton,  which 
consists  of  the  skull  including  the  gill  arches,  and  the  vertebral 
column  and  ribs*  and  the  appendicular  skeleton,  which  consists  of 
the  framework  of  the  fins. 

To  prepare  the  endoskeleton  for  study,  take  an  animal  which 
has  not  been  dissected,  open  the  body  cavity  without  cutting 
the  pectoral  or  the  pel  via*  girdle,  and  remove  the  viscera.  Im- 
merse the  animal  for  a  short  time  in  hot  water  in  order  to  soften 
the  tissues,  and  then  thoroughly  remove  the  muscles  from  the 
cartilages.  A  stiff  brush  is  useful  in  doing  this,  but  great  care 
must  be  exercised  not  to  injure  the  more  delicate  cartilages  of 
the  gill  arches  and  head.  The  skeleton  must  not  be  allowed  to 
get  dry  but  must  be  kept  in  water  or  formalin. 

The  axial  skeleton.  The  vertebral  column  consists  of  a  suc- 
cession of  vertebrae  closely  joined  together  by  ligaments ;  they 
are  also  connected  by  the  notochord,  —  a  soft  pulpy  mass  which 
runs  through  the  axis  of  the  vertebral  column,  filling  the  spaces 
between  the  vertebrae. 

Each  vertebra  is  made  up  of  a  cylindrical,  deeply  biconcave 
body  called  the  centrum,  to  which  are  attached  dorsal  and  either 
lateral  or  ventral  projections.  The  concavities  at  the  ends  of 
the  centrum  are  joined  by  a  central  canal,  and  this  hourglass- 
like  space  is  filled  with  the  notochord.  The  inner  surface  of  the 
centrum  is  calcified. 

The  dorsal  projections  of  the  centra  form  the  neural  arches; 
they  inclose  the  neural  canal,  within  which  lies  the  spinal  cord. 
Each  arch  consists  of  a  pair  of  neural  processes,  which  form  its 
sides,  and  two  small  median  neural  spines,  which  form  its  roof. 
Between  the  neural  processes  are  the  intercalary  processes,  which 
are  similar  to  them  in  shape  and  size. 

The  lateral  and  ventral  projections  of  the  centrum  are  respec- 
tively the  transverse  processes  and  the  haemal  processes,  which  are 
the  equivalents  of  each  other.  In  the  region  of  the  trunk  each 
centrum  bears  a  pair  of  transverse  processes  ;  these  are  lateral 


28  VERTEBRATE  ZOOLOGY 

or  latero-ventral  projections,  at  the  distal  end  of  each  of  which  is 
a  short  rib.  In  the  caudal  region,  however,  the  ribs  are  absent 
and  the  processes  project  ventrally  and  meet  in  the  median 
plane,  forming  the  haemal  arches.  Within  these  arches  lie  the 
caudal  artery  and  vein. 

Exercise  32.  Draw  the  following  views:  (a)  a  side  view  of 
several  consecutive  vertebrae;  (b)  an  end  view  of  a  trunk 
vertebra  with  the  ribs  belonging  to  it;  (c)  an  end  view  of 
a  caudal  vertebra. 

Exercise  33.  Split  a  portion  of  the  spinal  column  by  a  sagittal 
incision  and  draw  the  surface  exposed. 

The  skull  is  made  up  of  two  very  distinct  portions,  —  the 
cranium,  within  which  is  the  brain,  and  the  sides  of  which  are 
formed  by  the  capsules  containing  the  special  sense  organs,  and 
the  visceral  skeleton,  which  incloses  the  anterior  end  of  the 
alimentary  canal  and  forms  the  gill  arches  and  the  skeleton  of 
the  mouth.  Separate  the  cranium  from  the  visceral  skeleton 
and  thoroughly  clean  the  former. 

The  cranium  is  an  irregularly  shaped  case  of  cartilage.  The 
orbit  which  contains  the  eye  and  its  muscles  and  nerves  is  a 
long,  deep  depression  occupying  the  larger  part  of  the  side  of  it; 
behind  this  is  the  auditory  capsule,  which  forms  the  hinder  end 
of  the  skull;  in  front  of  it  is  the  nasal  capsule.  The  rostrum,  the 
framework  of  the  snout,  forms  the  anterior  end  of  the  skull. 
In  Mustelus  the  rostrum  is  formed  of  three  delicate  rods  of  car- 
tilage which  meet  at  their  forward  end;  in  Squalus  the  spaces 
between  the  rqds  are  closed  by  thin  plates  of  cartilage.  Just 
behind  the  nasal  capsule  on  each  side  is  a  large  foramen  through 
which  the  ophthalmic  branches  of  the  trigeminal  and  facial  nerves 
emerge  from  the  orbit.  At  the  hinder  end  of  the  skull  is  the 
foramen  magnum,  a  large  aperture  through  which  the  spinal  cord 
enters  the  brain  cavity.  In  the  dorsal  surface  of  the  hinder  part 
of  the  skull  is  a  deep  depression,  at  the  bottom  of  which  are  two 
small  holes  ;  these  are  the  openings  of  the  endolymphatic  ducts. 
In  the  dorsal  surface  of  the  forward  part  of  the  skull  is  the 


THE  DOGFISH  29 

anterior  fontanelle,  a  large  opening  into  the  brain-cavity  which 
is  closed  by  a  fibrous  membrane. 

Exercise  34.  Draw  the  dorsal  view. 

Study  the  lateral  aspect  of  the  skull.  Note  the  great  extent 
of  the  orbit  and  identify  the  following  foramina  in  it :  the  optic 
foramen,  a  large  hole  for  the  passage  of  the  optic  nerve,  which 
lies  near  the  middle  of  the  lower  margin  of  the  orbit ;  the  troch- 
lear  foramen,  a  small  hole  above  the  optic  foramen ;  the  anterior 
ophthalmic  foramen,  near  the  anterior  end  of  the  orbit  and  dorsally 
situated,  for  the  exit  from  the  orbit  of  the  ophthalmic  branches 
of  the  trigeminal  and  facial  nerves ;  the  large  trigeminal  foramen, 
at  the  hinder  end  of  the  orbit,  near  its  lower  margin,  for  the 
passage  of  the  trigeminal,  the  abducens,  and  a  part  of  the  facial 
nerves ;  the  large  facial  foramen,  above  the  trigeminal  foramen, 
for  the  passage  of  the  main  portion  of  the  facial  nerve ;  the 
small  oculomotor  foramen,  directly  in  front  of  the  trigeminal  fora- 
men. Besides  these  foramina  several  other  small  ones  are  present 
which  are  occupied  by  blood  vessels. 

Posterior  to  the  orbit  is  a  shallow,  longitudinal  groove  in  which 
the  anterior  cardinal  vein  lies  ;  the  glossopharyngeal  foramen  is  in  it. 

The  ventral  surface  of  the  cranium  is  broad  and  flat  poste- 
riorly, and  narrow  between  the  orbits.  It  is  crossed  near  the 
middle  by  two  grooves  in  which  arteries  lie.  At  its  anterior  end 
are  the  openings  of  the  nasal  capsules. 

Exercise  35.  Draw  a  side  view  of  the  cranium  and  carefully 
label  all  these  features. 

Exercise  36.  Draw  a  ventral  view  of  the  cranium. 

Observe  the  foramen  magnum.  On  either  side  of  it  are  the 
two  condyles  by  which  the  skull  articulates  with  the  trunk.  At 
the  side  of  each  condyle  is  the  foramen  of  the  vagus. 

The  visceral  skeleton.  This  consists  of  a  series  of  seven  arches 
beneath  the  cranium  and  the  anterior  end  of  the  vertebral  col- 
umn which  surround  the  pharynx  and  the  mouth.  Each  arch 
is  a  paired  structure  consisting  of  a  right  and  a  left  side  which 


30  VERTEBRATE  ZOOLOGY 

meet  in  the  midventral  plane ;  each  side  is  also  made  up  of  a 
dorsal  and  a  ventral  half. 

The  visceral  arches  fall  into  two  groups,  — an  anterior  group  con- 
sisting of  two  arches,  the  first  or  mandibular  arch  and  the  second 
or  hyoid  arch,  and  a  posterior  group  consisting  of  the  posterior  five 
arches,  all  of  which  support  gills  and  are  called  the  branchial  or  gill 
arches.  A  further  distinction  between  these  two  groups  is  that 
the  arches  constituting  the  first  alone  appear  as  a  portion  of 
the  head  proper,  those  constituting  the  second  group  having 
migrated  backward  into  the  trunk.  This  condition  is  a  secondary 
one  and  has  been  brought  about  by  the  shortening  of  the  dor- 
sal or  cranial  portion  of  the  hinder  part  of  the  skull  without 
a  corresponding  shortening  of  the  ventral  or  visceral  portion. 
The  primitive  position  of  all  the  visceral  arches  is  on  the  head. 

The  mandibular  arch  forms  the  jaws  of  the  animal.  The  dor- 
sal half,  or  upper  jaw,  is  formed  of  a  pair  of  cartilages  called 
the  pterygoquadrate  cartilages ;  the  ventral  half,  or  lower  jaw,  is 
formed  of  a  pair  called  Meckel's  cartilages.  Each  pterygoquadrate 
cartilage  is  joined  with  the  base  of  the  cranium  by  a  strong  liga- 
ment near  its  middle,  and  at  its  hinder  end  articulates  with 
the  lower  jaw.  The  two  halves  of  the  lower  jaw  are  joined  to- 
gether by  a  median  ligament.  The  jaws  are  also  joined  with  the 
second  or  hyoid  arch  by  means  of  a  ligament,  and  also  with 
the  base  of  the  cranium.  Slender,  accessory  labial  cartilages  are 
present  in  the  lips  at  the  side  of  both  the  upper  and  the  lower 
jaw,  two  pairs  being  in  the  former  and  one  in  the  latter. 

The  hyoid  arch  forms  the  principal  support,  or  suspensorium,  of 
the  jaws;  it  also  supports  the  tongue  and  bears  the  foremost 
pair  of  gills.  Its  dorsal  half  on  each  side  is  called  the  hyomandib- 
ular  cartilage;  it  projects  outward  from  the  cranium,  with  which 
it  articulates,  and  at  its  outer  end  is  joined  by  short  ligaments 
with  the  jaws  and  also  by  a  long  ligament  with  the  base  of  the 
cranium.  Projecting  from  its  hinder  border  are  several  deli- 
cate cartilaginous  rods  called  the  gill  rays,  which  support  the 
gill  filaments. 

The  ventral  half  of  the  hyoid  arch  on  each  side  is  called  the 
ceratohyal  cartilage ;  it  bears  gill  rays  on  its  hinder  border.  Joining 


THE  DOGFISH  31 

the  two  ceratohyals  ventrally  and  projecting  forward  is  the 
basihyal  cartilage,  which  supports  the  tongue. 

The  five  branchial  arches  are  essentially  alike  in  structure. 
Each  arch  is  divided  into  four  segments  on  each  side,  two  dor- 
sal and  two  ventral.  The  dorsal  elements  are  the  pharyngobran- 
chial  and  the  epibranchial  cartilages.  The  former  run  obliquely 
backward,  terminating  dorsally  beneath  the  spinal  column,  the 
posterior  two  pharyngobranchials  being  fused  together;  the 
latter  are  vertical  in  position  and  correspond  to  the  hyoman- 
dibular  cartilage.  The  ventral  elements  are  the  ceratobranchial 
and  the  hypobranchial  cartilages,  the  former  of  which  articulate 
with  the  epibranchials  in  the  midlateral  plane  and  the  latter  run 
obliquely  backward  to  meet  their  fellows  of  the  opposite  side 
in  the  midventral  line.  The  hypobranchials  are  not  all  alike. 
In  Mustelus  the  posterior  two  pairs  and  in  Squalus  the  posterior 
three  pairs  are  fused  together  and  with  the  fifth  ceratobranchials, 
forming  a  broad  median  plate  called  the  basibranchial  cartilage. 

The  epibranchials  and  ceratobranchials  of  the  first,  second, 
third,  and  fourth  branchial  arches  bear  gill  rays. 

Along  the  outer  sides  of  the  second,  third,  and  fourth  bran- 
chial arches  are  three  pairs  of  supernumerary  cartilages  called 
the  extrabranchials. 

Exercise  37.  Draw  a  semidiagrammatic  side  view  of  the  visceral 
skeleton. 

Exercise  38.  Draw  a  similar  ventral  view. 

The  appendicular  skeleton ;  the  median  fins.  The  median  fins 
are  an  anterior  dorsal  and  a  posterior  dorsal  fin,  a  ventral  fin 
(in  Mustelus  but  not  in  Squalus),  and  a  caudal  fin.  The  skele- 
ton of  the  dorsal  fins  consists  of  a  row  of  cartilaginous  fin  rays, 
the  bases  of  which  are  often  fused  together,  while  at  the  outer 
ends  are  a  number  of  small  plates  of  cartilage.  On  each  side  of 
these  fin  rays,  and  extending  beyond  them,  is  a  series  of  slender, 
horny  fibers  which  develop  in  the  skin  and  belong  to  the  exo- 
skeleton.  The  other  median  fins  possess  these  fibers  alone,  the 
cartilaginous  elements  being  much  reduced  or  entirely  absent. 


32  VEETEBKATE  ZOOLOGY 

The  paired  fins.  These  consist  of  the  pectoral  fins  and  the 
pelvic  fins,  which  are  supported  by  the  pectoral  and  pelvic 
girdles  respectively. 

The  pelvic  girdle  is  an  elongated  plate  of  cartilage  which 
extends  transversely  across  the  body  in  front  of  the  anus  and 
articulates  with  the  pelvic  fins.  The  skeleton  of  the  pelvic  fin 
consists  of  a  long,  more  or  less  curved  rod  of  cartilage  called 
the  basipterygium,  which  extends  straight  back  from  the  girdle. 
The  cartilaginous  fin  rays  articulate  with  this  and  the  girdle ;  the 
distal  portion  of  the  fin  is  supported  by  dermal  horny  rays. 

In  the  male  the  basipterygium  is  much  extended  by  the  addi- 
tion of  a  second  long  cartilaginous  rod  at  its  posterior  end, 
which  is  grooved  on  its  upper  surface  and  forms  the  clasper. 

Exercise  39.  Draw  the  pelvic  fin  and  girdle. 

The  pectoral  girdle  is  a  U-shaped  cartilaginous  arch  which  lies 
transversely  across  the  ventral  and  on  the  lateral  sides  of  the 
body,  immediately  back  of  the  gill  arches.  On  each  side  of  the 
ventral  portion  of  the  girdle  is  a  depression,  the  glenoid  fossa,  in 
which  the  fin  articulates,  and  which  divides  the  girdle  into  a 
dorsal  or  scapular  and  a  ventral  or  coracoid  portion. 

The  pectoral  fin  articulates  with  the  pectoral  girdle  by  three 
basal  cartilages,  the  propterygium,  the  mesopterygium,  and  the 
metapterygium,  of  which  the  last  named  is  the  hindermost. 
Along  the  outer  margkTbf  these  cartilages  is  a  series  of  carti- 
laginous fin  rays,  many  of  which  are  segmented ;  these  fin  rays 
do  not,  however,  support  the  entire  fin,  but  only  its  basal 
portion,  the  distal  half  being  supported  by  dermal  horny  rays. 

Exercise  40.  Draw  the  pectoral  girdle  and  fin  showing  exactly 
the  outlines  of  all  the  cartilages. 


THE  PEECH  33 


A  TELEOSTEAN  FISH.    THE  PERCH 

The  perch  is  one  of  the  commonest  fresh-water  fishes.  It  is 
found  almost  everywhere  in  streams,  ponds,  and  lakes,  where 
it  lives  on  small  aquatic  animals  of  every  kind.  Any  other 
bony  fish  may  be  used  in  place  of  the  perch ;  the  differences  in 
structure  which  exist  will  not  confuse  the  dissection.  Two  or 
three  specimens  will  be  needed  for  each  student;  during  the 
progress  of  the  dissection  they  should  be  kept  in  a  five  per  cent 
solution  of  formalin. 

Observe  the  form  and  external  markings  of  the  animal.  The 
body  of  the  perch,  like  that  of  the  majority  of  teleosts,  is  elon- 
gated and  laterally  compressed,  with  a  wedge-shaped  head  and 
a  terminal  mouth;  the  hinder  end  is  less  compressed  than  the 
forward  portion  and  terminates  with  a  homocercal  fin,  which  is 
the  principal  organ  of  locomotion.  The  other  fins  are  all  of 
good  size  and  may  be  used  both  for  purposes  of  locomotion  and 
as  a  means  of  defense  against  attack,  the  sharp  spines  with 
which  most  of  them  are  provided  being  formidable  weapons. 

The  entire  body,  with  the  exception  of  a  part  of  the  head  and 
the  fins,  is  covered  with  ctenoid  scales^  which  are  not  placed 
side  by  side,  as  are  the  placoid  scales  of  the  dogfish,  but  over- 
lap one  another  posteriorly.  Examine  them  carefully  on  differ- 
ent parts  of  the  body  and  note  their  arrangement  and  difference 
in  size.  If  the  fish  is  fresh,  note  the  slimy,  transparent  epider- 
mis which  covers  the  scales  ;  if  it  is  not  fresh,  scrape  off  some  of 
the  dried  epidermis.  Note  the  lateral  line  which  runs  along  each 
side  of  the  body  parallel  with  the  back  its  entire  length ;  it  is 
an  organ  of  special  sense. 

Observe  the  color  bands  and  their  arrangement.  Are  they 
bilaterally  symmetrical?  Note  that  the  color  consists  of  an 
aggregation  of  small  dots,  except  where  it  forms  solid  masses. 
These  dots  are  pigment  cells ;  they  are  just  beneath  the  epider- 
mis in  the  outer  layer  of  the  dermis  and  may  be  scraped  off 


34  VEKTEBKATE  ZOOLOGY 

with  the  epidermis.  Note  the  structure  of  a  single  dot;  it 
will  be  seen  to  consist  of  a  black  central  kernel,  —  the  body 
of  the  cell,  —  surrounded  by  a  halo  of  fine  dots  which  con- 
stitute its  outlying  projections.  Many  fishes  have  the  power 
of  changing  their  color  in  a  remarkable  degree,  although  it 
is  probably  a  reflex  action  in  them  and  not  under  the  con- 
trol of  the  will.  It  is  accomplished  by  the  often  very  rapid 
variation  in  the  extent  of  these  pigment  cells,  which  in  such 
cases  are  amreboid. 

The  body  may  be  divided  into  three  regions,  the  head,  trunk, 
and  tail,  —  the  boundary  between  the  latter  two  regions  being 
the  anus.  There  is  no  neck. 

Vertebrates  which  live  in  the  water  differ  much  from  those 
living  on  the  land  in  the  arrangement  of  the  body  regions. 
Water  animals  must  force  their  way  through  a  dense  medium, 
and  hence  the  forward  portion  of  the  body  is  rigid  and  usually 
more  or  less  wedge-shaped.  A  neck  region  is  thus  absent,  it  being 
essentially  a  flexible  one.  Even  in  those  mammals  which  have 
adapted  themselves  to  a  wholly  aquatic  life,  as  the  cetaceans, 
the  neck  region  is  so  much  reduced  that  the  head  and  trunk  are 
in  direct  contact  with  each  other.  In  every  animal  which  moves 
rapidly,  however,  at  least  one  flexible  body  region  must  be  pres- 
ent where  the  body  can  turn  when  the  direction  of  movement 
is  to  be  changed.  In  the  fish  this  is  accomplished  in  the^caudal 
region;  in  most  mammals  it  is  in  the  lumbar  region. 

The  head.  The  head  of  teleostean  fishes  differs  from  that  of 
land  vertebrates  in  that  it  contains  the  organs  of  respiration 
and  the  heart.  The  head  is  flattened  ventrally  and  dorsally,  with 
the  large  mouth  at  its  anterior  and  the  gills  at  its  posterior  end. 
The  opening  of  the  mouth  is  bounded  ventrally  by  the  paired 
mandibles,  and  dorsally  by  the  paired  premaxillae,  above  which  on 
each  side  is  the  flattened  maxilla.  The  large  eyes  are  without 
lids.  A  transparent  membrane  called  the  conjunctiva  passes  over 
the  front  of  the  eye  and  is  continuous  with  the  epidermal  layer 
of  the  skin ;  a  deep  fold  of  the  skin  is  also  present  around  the 
eye,  joining  it  with  the  skin  of  the  head,  and  yet  permitting  it 
considerable  freedom  of  motion  in  its  socket. 


THE  PERCH  35 

In  front  of  the  eyes  are  two  pairs  of  nostrils;  there  is,  how- 
ever, but  a  single  pair  of  nasal  capsules,  each  capsule  having 
two  external  openings.  Note  the  difference  in  shape  of  these 
two  nostrils  and  the  valve  which  overhangs  the  anterior  one. 
The  nasal  capsules  do  not  open  posteriorly  into  the  mouth,  but 
are  wholly  sensory  in  function. 

At  the  posterior  end  of  the  head  is  the  large  operculum,  or  gill 
cover,  and  at  its  hinder  margin,  the  gill  openings.  Note  the  sharp 
protective  spine  which  projects  back  from  each  operculum. 
Along  the  hinder  and  lower  border  of  the  operculum  is  the 
branchiostegal  membrane,  supported  by  seven  parallel  bony  rays, 
the  branchiostegal  rays,  which  forms  a  valve  guarding  the  gill 
opening.  Underneath  the  operculum  on  each  side  will  be  seen 
the  four  gill  arches,  which  bear  the  red  gills,  and  the  clefts  be- 
tween the  arches.  Note  the  rudimentary  gill,  the  pseudobranch, 
which  appears  as  a  red  patch  on  the  inner  surface  of  the  oper- 
culum in  front  of  the  first  gill  arch. 

Cut  off  the  left  operculum  and  probe  between  the  gill  clefts 
into  the  pharynx.  Observe  carefully  the  form  and  position  of 
the  gill  arches  and  the  double  row  of  gill  filaments  on  each; 
also  the  gill  rakers,  —  the  row  of  spiny  projections  on  the  side 
of  each  arch,  which  prevent  food  from  passing  through  the 
clefts.  In  the  elasmobranch  the  gill  clefts  are  not  covered  by 
an  operculum. 

The  trunk  and  caudal  region.  These  two  regions  pass  gradu- 
ally into  each  other;  they  bear  the  appendages.  At  the  posterior 
^end  of  the  trunk  are  the  anus  and  the  genital  and  urinary  pores. 
*The  anus  is  the  largest  and  most  anterior  of  these  three  open- 
ings ;  the  other  two  are  minute  and  are  situated  behind  it  on  a 
small  papilla.  Behind  this  is  often  a  transverse  depression.  ^ 

The  appendages.  Two  kinds  of  appendages  are  present, — the 
paired  fins  and  the  median  fins.  The  latter  are  the  more  primitive 
structures  and  are  alone  present  in  the  lowest  fishes;  they  are 
simply  dorsal  and  ventral  flattened  expansions  of  the  body, 
which  are  stiffened  by  bony  rays.  In  the  perch  two  dorsal  fins 
and  one  ventral  or  anal  fin  are  present,  and  one  homocercal  caudal 
fin.  Note  carefully  which  of  these  fins  have  sharp  spiny  rays, 


36  VERTEBRATE  ZOOLOGY 

and  in  which  the  ends  of  the  rays  are  divided  and  flexible. 
Observe  that  the  two  dorsal  fins  are  nearly  continuous  with 
each  other. 

The  paired  fins  are  also  expansions  of  the  body  wall,  stiffened 
by  bony  rays;  they  are  homologous  to  the  appendages  of  the 
higher  vertebrates.  Two  pairs  are  present, — an  anterior  pair,  the 
pectoral  fins ;  and  a  posterior  pair,  the  pelvic  fins.  The  former  are 
nearly  vertical  in  position  and  are  situated  on  the  side  of  the 
trunk  just  behind  the  operculum.  They  are  supported  by  a  bony 
arch  within  the  body  wall  just  back  of  the  gills,  which  is  called 
the  pectoral  girdle.  The  pelvic  fins  are  a  short  distance  behind 
them  and  are  nearly  horizontal  in  position.  In  the  more  primi- 
tive fishes  the  pelvic  fins  are  situated  just  in  front  of  the  anus. 
Note  that  in  all  the  fins  the  rays  with  split  tips  are  segmented. 

Exercise  1.  Draw  a  view  of  the  right  side  of  the  animal ;  do  not 
draw  the  scales.    Label  the  organs  carefully. 

Exercise  2.  Draw  the  ventral  view. 

The  internal  organs.  It  will  be  well  first  to  cut  off  the  sharp 
tips  of  the  dorsal  fins  to  keep  them  from  hurting  the  hands. 
The  internal  organs  will  be  exposed  by  removing  the  left  side 
of  the  body  wall.  After  placing  a  probe  in  the  anus  to  mark  it, 
make  a  straight  incision  through  the  body  wall  from  just  in 
front  of  the  anus  to  the  mouth,  cutting  through  the  midven- 
tral  point  of  the  lower  jaw.  Care  must  be  taken  not  to  cut  the 
organs  which  lie  in  the  body  cavity.  Make  then  a  deep  cut 
downward  and  inward  along  the  lateral  line  on  the  left  side 
of  the  body  until  the  scalpel  strikes  the  spinal  column  or  the 
basal  portion  of  the  ribs ;  cut  always  against  the  outer  edges  of 
the  scales,  from  behind  forward.  When  the  scalpel  will  go  no 
farther  pass  it  ventrally  along  the  outer  surface  of  the  ribs  and 
remove  the  muscles  of  the  side  of  the  body. 

Determine  now  definitely  the  position  of  the  spinal  column, 
since  it  marks  the  dorsal  boundary  of  the  abdominal  cavity,  and 
carefully  cut  away  the  entire  left  body  wall,  removing  thus  the 
ribs  with  any  muscles  which  may  still  .be  attached  to  them,  the 


THE  PERCH  37 

left  pectoral  fin  and  pectoral  girdle,  and  the  left  pelvic  fin.  It 
is  best  in  doing  this  to  work  from  the  midventral  incision 
upward,  as  in  this  way  the  internal  organs  are  brought  grad- 
ually into  view  as  the  work  proceeds.  The  liver,  intestine, 
and  reproductive  organs,  which  are  sometimes  very  large,  will 
first  be  seen ;  then,  dorsal  to  them,  the  air  bladder.  This  organ 
adheres  closely  to  the  body  wall  and  special  care  must  be  taken 
not  to  injure  it;  its  ventral  wall  forms  a  wall  across  the  body 
cavity  which  is  tough  and  strong,  its  lateral  walls  becoming 
thinner  dorsally. 

Having  removed  the  left  body  wall,  cut  away  with  scissors 
the  portion  of  the  right  body  wall  between  the  midventral  in- 
cision and  the  air  bladder. 

Place  the  animal  in  a  pan  of  water  and  examine  the  organs, 
without,  however,  disturbing  them.  Note  the  glistening  perito- 
neum,— the  membrane  which  lines  the  abdominal  cavity;  it  passes 
along  the  ventral  side  of  the  air  bladder.  The  mesenteries,  the 
membranes  which  support  the  intestine  and  the  other  organs  in 
the  abdominal  cavity,  are  folds  of  the  peritoneum. 

The  body  cavity  is  made  up  of  two  divisions,  the  larger  and 
posterior  of  which  is  the  abdominal  cavity,  the  anterior  and  very 
much  smaller  one  being  the  pericardial  cavity.  The  former  is 
lined  by  the  peritoneum  and  contains  most  of  the  viscera;  the 
latter  is  lined  by  the  pericardium  and  contains  the  heart.  These 
two  cavities  are  separated  from  each  other  by  the  false  diaphragm, 
which  is  composed  of  the  posterior  wall  of  the  pericardium  and 
the  anterior  wall  of  the  peritoneum;  it  is  not  homologous  to 
the  diaphragm  of  mammals. 

In  the  abdominal  cavity  the  largest  organ  is  the  air  bladder, 
which  extends  the  entire  length  of  the  cavity  and  occupies  the 
dorsal  half  of  its  space.  In  the  perch  it  is  a  simple  sac  which 
is  not  connected  with  the  pharynx  by  a  duct,  as  is  the  case  in 
the  trout,  catfish,  and  many  other  fishes.  On  the  inner  surface 
of  its  ventral  wall  a  pair  of  red  patches  composed  of  a  network 
of  capillaries  will  be  noticed.  The  air  bladder  is  a  hydrostatical 
apparatus  by  means  of  which  the  fish  can  maintain  its  position 
in  the  water  at  different  depths  without  conscious  effort. 


38  VERTEBRATE  ZOOLOGY 

At  the  anterior  end  of  the  abdominal  cavity  and  just  back  of 
the  false  diaphragm  is  the  large  red  liver  ;  at  the  posterior  end, 
running  back  to  the  anus,  is  the  intestine,  which  is  usually 
inclosed  in  fat.  The  anterior  portion  of  the  intestine  forms 
a  coil  lying  a  little  to  the  right  of  the  median  plane,  within 
which,  often  imbedded  in  fat,  lies  the  spleen.  On  the  animal's 
left,  more  or  less  covered  by  the  hinder  border  of  the  liver,  is 
the  stomach,  a  large  cylindrical  body ;  alongside  of  it  are  several 
elongated  pyloric  appendages. 

The  gonads,  or  genital  glands,  which  consist  of  the  paired  testes 
in  the  male  and  the  single  ovary  in  the  female,  vary  much  in 
size  at  different  seasons  of  the  year.  They  are  often  very  large 
and  may  occupy  a  large  portion  of  the  abdominal  cavity.  They 
will  be  seen  just  dorsal  to  the  intestine,  extending  from  the 
hinder  end  of  the  cavity  forward. 

In  the  pericardial  cavity,  beneath  (dorsal  to)  the  thick  muscles 
between  the  gills,  will  be  seen  the  heart.  It  consists  of  the 
median  ventricle,  a  large  muscular  organ,  at  the  sides  of  which 
appears  the  deep  red  auricle ;  at  the  back  of  (dorsal  to)  this  organ 
is  the  sinus  venosus,  a  large,  deep  red  sac  which  communicates 
with  the  auricle.  In  front  of  the  ventricle  is  the  large  bulbus 
arteriosus  which  is  the  beginning  of  the  aorta. 

Exercise  3.  Make  a  semidiagrammatic  sketch  of  the  left  side  of 
the  fish,  showing  the  opened  body  cavity  and  its  organs  as 
they  appear  before  they  have  been  disturbed  ;  label  them  all 
carefully. 

The  digestive  system.  This  consists  of  the  mouth,  pharynx, 
oesophagus,  stomach  with  the  pyloric  appendages,  intestine,  and 
liver ;  a  pancreas  may  also  be  present. 

The  mouth  and  pharynx.  Cut  away  the  left  half  of  the  lower 
jaw  and  the  gill  arches,  but  do  not  injure  the  heart ;  the  mouth 
and  pharynx  are  thus  fully  exposed.  They  will  be  seen  to  form 
a  single  large  space  extending  from  the  opening  of  the  mouth 
to  the  oesophagus,  the  pharynx  being  the  portion  of  the  space 
which  contains  the  gills. 


THE  PEKCH  39 

The  teeth  are  very  small  and  are  present  not  only  in  the 
upper  and  lower  jaws  but  also  on  the  roof  of  the  mouth  and 
the  roof  and  floor  of  the  pharynx.  Examine  them  carefully  with 
the  aid  of  a  hand  lens.  There  are  three  groups  of  teeth  on  the 
roof  of  the  mouth,  a  small  median  patch  of  vomerine  teeth,  and 
a  pair  of  lateral  patches  of  maxillary  teeth.  Note  carefully  the 
position  of  the  teeth  on  the  gill  arches. 

Just  within  the  margin  of  each  jaw  is  a  transverse  membrane ; 
probe  behind  them.  These  two  membranes  are  the  oral  valves, 
which  prevent  the  water  from  flowing  out  again  through  the 
mouth  during  respiration.  Breathing  consists  of  two  actions, — 
the  inspiration  and  the  expiration.  At  the  inspiration  the  oral 
valves  open  and  the  branchiostegal  membranes,  which  form 
valves  at  the  opening  of  the  operculum  on  each  side,  close  ;  at 
the  expiration  the  oral  valves  close  and  the  branchiostegal  valves 
open,  allowing  the  respiratory  water  to  pass  out  through  the 
gill  clefts. 

Observe  carefully  the  form  and  arrangement  of  the  gill  arches. 
Note  the  gill  rakers, — the  short  spiny  projections  on  the  gill  arches 
which  prevent  solid  substances  from  passing  out  through  the 
gill  clefts.  Cut  out  a  gill  arch  and  examine  the  gills  on  it. 
Observe  that  a  double  row  of  gill  filaments  is  present.  Study 
carefully  the  arrangement  of  these  filaments  with  reference  to 
the  gill  arch  and  with  reference  to  each  other.  In  fishes  the 
gills  are  outgrowths  of  the  wall  of  the  pharynx.  In  the  ven- 
tral wall  of  the  mouth  is  the  tongue;  note  its  relation  to  the 
gill  arches. 

Exercise  4.  Draw  a  sketch  of  the  mouth  and  pharynx,  showing 
both  dorsal  and  ventral  surfaces  with  the  features  above 
described. 

Exercise  5.  Draw  a  diagram  of  a  gill  arch  with  its  two  rows  of 
gill  filaments. 

Study  the  remainder  of  the  digestive  tract.  Observe  the 
short,  wide  oasophagus,  which  joins  the  pharynx  with  the 
stomach.  Turn  the  left  lobe  of  the  liver  to  one  side  and  observe 


40  VERTEBRATE   ZOOLOGY 

the  anterior  or  cardiac  end  of  the  stomach.  Note  the  shape  of  the 
liver  and  the  mesentery  which  attaches  it  to  the  anterior  abdom- 
inal wall ;  cut  this  mesentery.  Note  the  mesentery  which  joins 
the  stomach  with  the  ventral  wall  of  the  air  bladder,  and  cut  it. 
Note  that  a  part  of  the  intestine  lies  free  and  is  not  attached  to 
the  body  wall  by  a  mesentery.  Cut  the  oesophagus  and  remove 
the  entire  digestive  tract  from  the  body,  retaining,  however,  its 
posterior  attachment  at  the  anus. 

Study  its  various  parts.  The  stomach  has  three  distinct 
regions,  —  an  anterior  region,  which  extends  straight  back  from 
its  cardiac  portion  and  ends  posteriorly  in  a  blind  sac ;  a  pos- 
terior region,  which  leaves  the  anterior  region  at  right  angles 
near  its  middle  and  extends  to  the  beginning  of  the  intestine ; 
and  the  pyloric  appendages,  three  long,  cylindrical  blind  sacs.  Just 
back  of  these  appendages  is  a  slight  constriction  which  marks 
the  pyloric  or  hinder  end  of  the  stomach. 

The  intestine  begins  at  the  pylorus  and  extends  to  the  anus. 
It  is  composed  of  three  divisions :  the  duodenum  (which  includes 
the  anterior  loop  of  the  intestine,  between  the  limbs  of  which 
the  spleen  lies),  the  small  intestine,  and  the  rectum, — the  boundary 
between  the  last  two  divisions  being  the  circular  ridge  about 
an  inch  in  front  of  the  anus.  The  liver  is  a  large  gland  which 
communicates  with  the  intestine  by  means  of  the  bile  duct.  This 
duct  emerges  from  the  gall  bladder,  which  lies  against  the  pos- 
terior surface  of  the  liver,  receives  a  number  of  branch  ducts 
from  the  liver,  and  joins  the  intestine  near  the  base  of  the 
pyloric  appendages.  A  pancreas  has  not  been  found. 

Exercise  6.  Draw  a  semidiagrammatic  sketch  of  the  digestive 

tract  and  label  carefully  all  of  its  parts. 

Slit  open  the  stomach  and  a  portion  of  the  intestine  and 
examine  their  inner  surface. 

The  urogenital  system ;  the  male  genital  organs.  The  testes 
are  a  pair  of  white,  elongated  bodies  which  lie  in  the  abdominal 
cavity  just  ventral  to  the  air  bladder,  to  which  they  are  joined 
by  a  mesentery.  They  taper  towards  the  hinder  end  and  finally 
fuse  together,  the  median  portion  thus  formed  passing  directly 


THE  PERCH  41 

to  the  genital  pore  just  behind  the  anus.  The  actual  size  of  the 
testes  depends  upon  the  sexual  condition  of  the  animal ;  during 
the  breeding  season  they  are  large  and  may  extend  into  the 
anterior  portion  of  the  abdominal  cavity. 

The  female  genital  organs.  The  ovary  is  a  median  body  which 
lies  in  the  abdominal  cavity  between  the  intestine  and  the  air 
bladder,  and  is  joined  to  the  latter  by  a  mesentery.  It  is  an 
elongated  sac  filled  with  small  ova  and  varies  in  size  with'the 
sexual  condition  of  the  animal;  no  oviduct  is  present,  the  hinder 
part  of  the  ovary  becoming  gradually  smaller  and  finally  com- 
municating with  the  outside  through  the  genital  pore  just  back 
of  the  anus. 

Exercise  7.  Make  a  sketch  of  the  genital  organs. 

The  urinary  organs.  Remove  the  testes  or  the  ovary.  Dis- 
sect the  air  bladder  away  from  the  body  wall  and  remove  it. 
Note  the  thinness  of  its  dorsal  wall,  where  it  lies  just  beneath 
the  kidneys.  These  organs  are  a  pair  of  slender  deep  red  bands 
which  lie  close  against  the  dorsal  body  wall,  one  on  each  side 
of  the  vertebral  column.  Their  anterior  ends  unite  just  dorsal 
to  the  oesophagus  and  form  a  large,  dark-colored  median  mass 
called  the  head  kidney,  which  extends  across  the  body  cavity. 
Dissect  away  the  remains  of  the  oesophagus  and  note  the  exact 
shape  and  extent  of  the  head  kidney.  The  ureters  are  a  pair  of 
tubes  which  run  along  the  entire  length  of  the  medial  borders 
of  the  kidneys,  joining  at  their  hinder  ends.  The  single  vessel 
thus  formed  then  passes  to  the  minute  urinary  pore  just  back  of 
the  genital  pore ;  a  small  urinary  bladder  projects  from  the  median 
portion  of  the  ureters. 

Exercise  8.  Draw  a  sketch  of  the  urinary  system  within  an  out- 
line of  the  body  and  the  body  cavity. 

The  nervous  system  consists  of  (1)  the  central  nervous  system, 
which  includes  the  brain  and  the  spinal  cord;  (2)  the  peripheral 
nervous  system,  which  includes  the  paired  cranial  and  spinal 
nerves  and  the  sympathetic  nervous  system ;  and  (3)  the  special 
sense  organs. 


42  VERTEBRATE   ZOOLOGY 

We  shall  study  first  the  special  sense  organs ;  they  are  the  integu- 
mentary sense  organs,  the  nasal  organs,  the  eyes,  and  the  ears. 

The  integumentary  sense  organs  consist  of  (a)  minute  scattered 
sense  buds  which  occur  principally  on  the  head  but  also  on  the 
body,  and  (b)  of  the  lateral  line.  This  line  is  a  straight  canal  in 
the  integument  which  extends  along  the  side  of  the  body  from 
the  head  to  the  caudal  fin,  with  branches  also  upon  the  head, 
in  which  are  groups  of  sensory  cells.  At  regular  intervals  are 
minute  openings  to  the  outside  through  the  scales ;  each  scale 
covering  the  lateral  line  has  a  canal  on  its  inner  side  which  is 
a  branch  of  the  main  canal  and  communicates  with  the  outside 
through  a  pore  at  its  hinder  end. 

The  nasal  capsules  are  a  pair  of  sacs  situated  in  front  of  the  eyes 
and  communicating  with  the  outside  by  two  nostrils  on  each  side; 
no  communication  with  the  mouth  is  present.  Cut  off  the  outer 
wall  of  one  of  the  capsules  and  observe  the  delicate  folds  of  the 
sensory  epithelium  radiating  from  a  central  point. 

Exercise  9.  Make  a  drawing  of  the  capsule  on  a  large  scale. 

Cut  away  the  folds  of  the  capsule  and  observe  the  olfactory 
nerve  which  enters  it  at  its  hinder  side. 

The  eyes.  Observe  the  central  pupil  of  the  eye  through  which 
light  is  admitted  to  the  interior  of  it,  the  iris  which  surrounds 
the  pupil,  and  the  transparent  cornea  which  lies  in  front  of  both 
and  forms  the  outer  coating  of  the  eye.  Observe  carefully  the 
circular  fold  of  the  skin  which  surrounds  the  front  of  the  eyeball. 

With  strong  scissors  cut  away  the  circular  ridge  of  the  skull 
which  surrounds  the  eye,  and  remove  the  muscles  of  the  head 
just  beneath  and  back  of  it.  Remove  also  the  slimy  fold  of  the 
skin  just  mentioned,  which  surrounds  the  front  of  the  eye. 
Note  that  a  transparent  layer  of  the  skin  passes  over  the  cornea 
and  may  be  peeled  off ;  this  is  the  conjunctiva. 

Observe  the  position  of  the  eye  in  the  orbit ;  it  is  held  in 
place  by  the  optic  nerve,  which  joins  it  at  its  inner  end,  and  by 
six  small  muscles.  These  muscles  have  their  origin  in  the  wall 
of  the  orbit,  and  their  insertion  in  the  outer  coating  of  the  eye- 
ball, the  movements  of  which  they  control. 


THE  PERCH  43 

Study  these  muscles.  Press  the  eyeball  downward  and  note 
on  its  medial  side  the  insertions  of  two  muscles ;  the  anterior 
one  is  the  superior  oblique,  which  goes  from  the  eyeball  to  the 
inner,  anterior  wall  of  the  orbit ;  the  posterior  one  is  the  superior 
rectus,  which  goes  from  the  eyeball  to  the  inner,  posterior  wall 
of  the  orbit.  Push  the  eyeball  backward  and  note  the  inferior 
oblique  muscle,  which  has  its  insertion  on  its  an tero- ventral 
surface  and  passes  parallel  with  the  superior  oblique  to  the  in- 
ner, anterior  wall  of  the  orbit.  On  the  posterior  side  of  the  eye- 
ball is  the  insertion  of  the  external  rectus  muscle,  which  runs  to 
the  inner,  posterior  wall  of  the  orbit.  Cut  the  superior  oblique 
muscle  at  its  insertion  in  the  eyeball ;  beneath  it  will  be  seen 
the  insertion  of  the  internal  rectus,  which  runs  back  to  the  inner, 
posterior  wall  of  the  orbit.  Cut  all  these  muscles  at  their  in- 
sertion in  the  eyeball  and  pull  it  gently  outward  and  forward ; 
the  inferior  rectus  will  be  seen,  whose  insertion  is  on  the  inner 
side  of  the  eyeball  and  which  runs  to  the  inner  posterior  wall 
of  the  orbit.  Cut  this  muscle  and  the  optic  nerve  and  remove 
the  eyeball  from  the  orbit.  Note  the  origins  of  the  four  rectus 
muscles  in  the  posterior  wall  of  the  orbit,  and  of  the  two  oblique 
muscles  in  the  forward  wall  of  the  orbit. 

Exercise  10.  Draw  a  sketch  of  the  orbit,  showing  its  muscles 
and  the  optic  nerve. 

Study  the  eyeball.  Its  tough  outer  covering  is  the  sclerotic 
coat,  or  the  sclera,  of  which  the  cornea  is  the  portion  in  front.  Cut 
it  in  two  lateral  halves  ;  remove  the  other  eye  and  cut  it  in  an 
anterior  and  a  posterior  half  ;  study  the  interior  of  both  under 
water.  Just  back  of  the  pupil  is  the  spherical  crystalline  lens ;  do 
not  remove  it.  This  is  the  shape  of  the  lens  in  all  vertebrates 
which  live  under  water.  In  a  dense  medium  like  water  vision 
is  necessarily  limited  in  range,  and  fishes  can  only  see  objects 
which  are  close  to  them.  An  eye  with  a  spherical  lens  is 
shortsighted. 

The  inner  coating  of  the  eye  is  the  retina.  Between  it  and 
the  sclerotic  coat  is  the  choroid  coat.  This  consists  of  three  layers, 
—  the  black  pigment  layer  which  lies  just  beneath  the  retina,  the 


44  VEETEBEATE   ZOOLOGY 

glistening  silvery  layer  which  is  just  within  the  solera,  and 
the  vascular  layer  which  contains  blood  vessels.  Around  the 
entrance  of  the  optic  nerve  the  vascular  layer  is  much  thickened. 
The  portion  of  the  choroid  which  extends  over  the  front  of  the 
eye  is  the  iris,  the  central  opening  of  which  is  the  pupil  ; 
delicate  muscles  in  the  iris  control  the  size  of  the  pupil. 
Around  the  inner  side  of  the  iris  a  ridge  called  the  ciliary  process 
extends  to  the  lens,  and  is  continuous  with  the  delicate  mem- 
brane in  which  the  lens  is  suspended. 

Note  the  blind  spot,  the  point  where  the  optic  nerve  enters 
the  eye.  From  near  this  spot  a  slender  projection  of  the 
choroid,  called  the  falciform  process,  which  ends  in  an  enlarge- 
ment called  the  campanula  Halleri,  extends  through  the  retina 
to  the  side  of  the  lens,  to  which  it  is  attached.  The  cam- 
panula contains  smooth  muscle  fibers  by  the  action  of  which 
the  position  of  the  lens  is  slightly  changed  and  its  focus 
altered.  The  range  of  accommodation  is,  however,  very  small. 
Use  the  hand  lens  in  studying  the  falciform  process ;  it  is 
usually  easily  found. 

The  two  large  chambers  of  the  eye  are  the  one  between  the 
iris  and  the  cornea,  which  is  filled  with  the  watery  aqueous  humor, 
and  that  between  the  retina  and  the  lens,  which  is  filled  with 
the  jellylike  vitreous  humor. 

Exercise  11.    Draw   a   diagram   representing   the   structure  of 
the  eye. 

The  ear.  The  auditory  organ  consists  of  the  membranous 
labyrinth  alone,  which  is  imbedded  in  the  cranium  back  of  the 
eye;  no  external  opening  exists.  To  dissect  it  out  is  a  difficult 
task,  but  with  care  and  patience  it  can  be  done.  The  auditory 
capsule,  which  contains  the  membranous  labyrinth,  is  an  exten- 
sive cavity  in  the  cranium,  which  is  in  communication  with  the 
brain  cavity ;  it  also  contains  the  peculiar  granular,  fatty  matter 
which  fills  the  brain  cavity.  The  labyrinth  is  imbedded  partly 
in  this  fatty  matter  and  partly  in  cartilage.  It  is  made  up  of 
the  saclike  vestibule,  three  semicircular  canals,  and  an  endo- 
lymphatic  duct  '  f 


THE  PERCH  45 

Carefully  shave  away  the  bony  wall  of  the  skull  just  back  of 
the  orbit,  and  look  first  for  the  semicircular  canals.  Two  of  these 
are  vertical  in  position  and  rise  to  the  dorsal  wall  of  the  skull, 
the  anterior  and  larger  of  the  two  being  imbedded  in  the  gran- 
ular, fatty  matter,  and  the  posterior  one  being  inclosed  in  car- 
tilage. Having  found  these  canals  and  dissected  them  free, 
look  for  the  third  semicircular  canal,  which  has  a  horizontal 
position.  Note  that  one  end  of  each  canal  is  swollen ;  this  is 
the  ampulla. 

The  semicircular  canals  project  from  the  vestibule.  This  is  a 
saccular  structure  which  is  composed  of  two  parts,  the  utriculus 
and  the  sacculus,  the  latter  being  ventral  to  the  former,  and 
being  nearly  filled  by  a  single  very  large  otolith,  —  a  flattened, 
very  hard,  bony  structure,  with  prominent  serrations  at  its 
hinder  end.  At  the  anterior  end  of  the  sacculus  is  a  small 
pocket  containing  a  minute  otolith  called  the  lagena ;  this  is  the 
structure  which  in  mammals  becomes  the  cochlea.  The  endo- 
lymphatic  duct  is  a  very  slender,  straight  tube,  which  passes 
dorsally  from  the  sacculus  and  ends  blind.  It  is  the  remains 
of  the  embryonic  invagination  which  during  the  development 
of  the  animal  resulted  in  the  formation  of  the  membranous 
labyrinth. 

Another  method  of  dissecting  the  ear  is  to  split  the  skull  and 
brain  by  an  incision  in  the  sagittal  plane,  to  remove  the  brain, 
and  then  carefully  scrape  away  the  fatty  matter  at  the  intersec- 
tion of  the  auditory  and  the  brain  cavities  until  the  membranous 
labyrinth  is  exposed. 

The  ear  in  most  fishes  is  not  an  organ  of  hearing  but  of  equi- 
libration,  its  function  being  to  enable  the  animal  to  maintain 
the  proper  position  in  the  water. 

Exercise  12.  Draw  the  membranous  labyrinth,  so  far  as  observed. 

The  brain.  If  the  brain  has  been  kept  in  strong  formalin,  as 
directed,  it  will  have  been  hardened  and  will  be  in  good  condi- 
tion for  dissection;  if,  however,  its  condition  is  for  any  reason 
no  longer  suitable,  a  fresh  animal  must  be  taken. 


46  VEKTE13EATE  ZOOLOGY 

Remove  all  the  skin  and  the  thick  muscles  from  the  head  and 
the  high-arched  dorsal  portion  of  the  trunk  just  back  of  it. 
With  a  strong  scalpel  or  scissors  cut  away  the  roof  of  the  skull 
and  the  dorsal  wall  of  the  neural  canal  of  the  spinal  column. 
The  brain  does  not  nearly  fill  the  cavity  of  the  skull  but  is  sur- 
rounded by  the  granular,  fatty  tissue  already  mentioned ;  care- 
fully remove  this  substance  and  expose  the  brain. 

Study  its  dorsal  surface.  It  is  made  up  of  five  divisions. 
The  first  and  anterior  division  is  the  cerebrum ;  it  consists  of  a 
pair  of  hemispheres,  at  the  anterior  ends  of  which  project  the 
olfactory  lobes.  The  third  division,  or  midbrain,  consists  of  the 
paired  optic  lobes,  the  largest  part  of  the  brain,  between  which 
and  the  cerebrum  appears  a  small,  median,  sunken  area,  —  the 
thalamencephalon,  the  second  division.  Projecting  dorsally  from 
this  division  is  the  long  and  slender  pineal  body,  or  epiphysis, 
which  is  the  rudiment  of  a  third  optic  nerve ;  it  may  have  been 
removed  in  exposing  the  brain.  Back  of  the  optic  lobes  are  the 
fourth  division,  the  cerebellum,  and  the  fifth  division,  the  medulla 
oblongata,  which  is  continuous  with  the  spinal  cord.  Note  the  longi- 
tudinal median  groove  in  the  medulla  and  spinal  cord,  and  the 
paired  lateral  swellings,  the  restiform  bodies,  at  the  anterior  end 
of  the  former. 

Exercise  13.  Draw  a  dorsal  view  of  the  brain  on  a  scale  of  3  or  4. 

Carefully  cut  away  one  side  of  the  skull  and  expose  the  side 
of  the  brain.  Find  the  ten  cranial  nerves.  The  first  nerve  is  the 
long  olfactory,  which  passes  forward  from  the  olfactory  lobe  to 
the  nasal  capsule.  The  second  is  the  optic  nerve,  which  arises 
just  in  front  of  the  optic  lobe  from  the  ventral  surface  of  the 
thalamencephalon ;  the  two  optic  nerves  cross  each  other  imme- 
diately, forming  the  optic  chiasma,  and  pass  each  to  the  eye  on 
the  opposite  side  of  the  body.  By  carefully  pressing  the  floor 
of  the  brain  case  away  from  the  brain  the  root  of  the  optic  nerve 
will  be  seen ;  the  nerve  may  then  be  traced  to  the  optic  foramen 
where  it  enters  the  orbit.  The  third  cranial  nerve,  the  oculomotor, 
is  a  small  nerve  which  will  be  seen  arising  on  the  ventral  surface 
of  the  brain  beneath  the  optic  lobe  and  passing  forward  to  the 


THE  PERCH  47 

orbit,  which  it  enters  back  of  the  optic  foramen.  The  fourth 
nerve,  the  trochlear,  is  about  the  size  of  the  third,  and  will  be 
seen  arising  just  back  of  the  optic  lobe  on  the  side  of  the  brain 
and  passing  forward  to  the  orbit,  which  it  enters  above  the 
optic  foramen. 

The  fifth  nerve,  the  trigeminal,  and  the  seventh,  the  facial,  arise 
together,  although  without  any  intermingling  of  their  fibers, 
from  the  side  of  the  anterior  end  of  the  medulla;  this  common 
root  will  be  easily  recognized  by  its  large  size.  The  two  nerves 
leave  the  cranium  together.  The  trigeminal  then  splits  up  into 
the  following  three  nerves:  (1)  the  ophthalmic  nerve,  which  passes 
forward  along  the  wall  of  the  orbit,  dorsal  to  the  optic  nerve,  to 
the  anterior  surface  of  the  head;  (2)  the  maxillary  nerve,  which 
goes  to  the  upper  jaw ;  and  (3)  the  mandibular  nerve,  which  goes 
to  the  lower  jaw.  The  facial  nerve  passes  backward  and,  divid- 
ing into  branches,  supplies  the  lower  jaw,  the  operculum,  and 
the  branchiostegal  membrane. 

The  sixth  nerves,  the  abducens,  are  a  pair  of  very  small  nerves 
which  arise  near  the  midventral  line  of  the  brain  and  pass  to 
the  orbits  ;  they  may  be  seen  when  the  ventral  surface  of  the 
brain  is  studied.  The  eighth  nerve,  the  auditory,  arises  on  the 
side  of  the  medulla  just  back  of  the  common  root  of  the  tri- 
geminal and  facial  nerves  ;  it  at  once  divides  into  three  branches 
which  go  to  the  auditory  capsule.  The  ninth  nerve,  the  glosso- 
pharyngeal,  and  the  tenth,  the  vagus  or  pneumogastric,  arise  together 
on  the  side  of  the  medulla  by  three  roots.  The  smallest  of 
these  roots  is  the  glossopharyngeal  nerve,  which  passes  back- 
ward to  the  first  gill  arch.  The  two  largest  roots  join  and 
form  the  vagus  nerve,  which,  passing  posteriorly,  supplies  the 
gill  arches,  except  the  first,  and  the  heart,  stomach,  and  lateral 
line.  Follow  it  and  its  branches  as  far  as  possible. 

Exercise  14.  Draw  the  side  view  of  the  brain  and  the  cranial 
nerves  so  far  as  observed,  on  a  scale  of  3  or  4. 

Cut  the  olfactory  nerves ;  loosen  the  brain  from  its  attach- 
ments, bend  it  back,  and  remove  it  from  the  body.  Study  its 


48  VERTEBRATE   ZOOLOGY 

ventral  surface.  At  its  anterior  end  will  be  seen  the  small 
hemispheres  with  the  olfactory  lobes  at  their  anterior  ends.  Back  of 
them  is  the  thalamencephalon,  from  which  project  the  following 
structures :  (a)  the  optic  nerves  with  the  optic  chiasma,  and  (b)  the 
median  infundibulum,  at  the  lower  end  of  which  is  the  hypophysis 
or  pituitary  body,  and  at  whose  sides  are  a  pair  of  large  swellings 
called  the  lobi  inferiores.  At  the  side  of  each  of  these  swellings 
on  the  ventral  surface  of  the  brain  the  oculomotor  nerve  arises, 
while  posterior  to  them  is  the  medulla  oblongata.  Note  the  median 
furrow  in  it  and  the  roots  of  the  delicate  abducens,  near  the  median 
line.  Identify  the  roots  of  the  other  cranial  nerves. 

Exercise  15.  Draw  the  ventral  aspect  of  the  brain  on  a  scale  of 
3  or  4. 

Cut  the  brain  in  two  in  exactly  the  sagittal  plane  and  study 
the  cut  surface.  The  brain  is  a  hollow  structure;  in  it  is  a 
series  of  cavities  which  are  a  continuation  of  the  central  canal 
of  the  spinal  cord.  The  most  posterior  of  these  cavities,  which 
is  directly  continuous  with  the  central  canal,  is  in  the  medulla, 
and  is  called  the  fourth  ventricle ;  the  cerebellum  projects  partly 
over  it.  Note  the  thick  ventral  wall  and  the  thin  dorsal  wall  of 
this  ventricle.  Note  also  that  the  cerebellum  is  solid  and  that 
beneath  it  the  fourth  ventricle  continues  forward  between  the 
optic  lobes,  forming  a  canal  called  the  aqueductus  Sylvii;  this 
canal  goes  to  the  thalamencephalon,  where  it  is  called  the 
third  ventricle. 

The  optic  lobes  are  hollow,  the  cavity  in  them  communicat- 
ing with  the  aqueductus  Sylvii.  On  the  floor  of  each  lobe  is  a 
crescent-shaped  ridge  called  the  torus.  A  W-shaped  median  fold 
of  the  posterior  wall  of  the  lobes  will  be  seen  between  the  two 
tori,  and  in  front  of  it  a  median  fold  of  the  anterior  wall.  Care- 
fully remove  the  thin  dorsal  wall  of  one  of  the  lobes  and  study 
these  structures. 

In  the  two  hemispheres  are  the  first  and  second,  or  lateral,  ven- 
tricles, which  are  shallow  spaces  communicating  with  the  third 
ventricle.  Make  a  transverse  section  of  one  of  the  hemispheres 


THE  PEECH  49 

and  note  the  floor  of  its  ventricle ;  this  is  much  thickened  and 
is  called  the  corpus  striatum. 

Exercise  16.  Draw  the  sagittal  section  on  a  scale  of  3  or  4. 

The  vascular  system.  This  is  made  up  of  the  following 
organs:  (1)  the  heart,  which  receives  venous  blood  from  the 
tissues  and  forwards  it  to  the  gills ;  (2)  the  arteries,  which  carry 
(a)  venous  blood  from  the  heart  to  the  gills,  and  (b)  arterial 
blood  from  the  gills  to  the  tissues ;  (3)  the  Veins,  which  carry 
venous  blood  to  the  heart ;  and  (4)  the  capillaries. 

The  veins.  Two  distinct  systems  of  veins  are  present,  one 
of  which  is  composed  of  the  systemic  veins,  which  carry  blood 
directly  to  the  heart;  the  other  is  composed  of  those  which 
carry  blood  first  to  the  liver,  and  is  called  the  portal  system. 

We  shall  first  study  the  latter  system.  Take  a  fresh  animal 
and  open  its  body  cavity  by  a  midventral  incision.  Cut  away 
both  the  right  and  the  left  body  walls  between  the  incision  and 
the  air  bladder.  The  portal  system  consists  of  a  pair  of  intestinal 
veins  which  lie  alongside  the  intestine,  a  splenic  vein  from  the 
spleen,  several  gastric  veins  from  the  stomach,  and  a  pneumatocystic 
vein  from  the  air  bladder,  all  of  which  unite  to  form  the  single 
large  portal  vein.  This  vein  passes  to  the  hinder  surface  of  the 
liver,  where  it  breaks  into  brandies  which  carry  the  blood  to  all 
parts  of  that  organ. 

The  veins  of  this  system  are  often  difficult  to  dissect  because 
of  the  fat  in  which  they  usually  lie  imbedded.  First  find  the 
two  intestinal  veins  and  free  them  from  the  fat.  Lift  up  the 
spleen  and  the  duodenal  loop  in  which  it  lies  and  find  the  point 
of  union  of  these  two  veins ;  find  also  the  splenic  vein,  the  gas- 
tric veins  from  the  stomach  proper  and  the  pyloric  appendages, 
and  the  pneumatocystic  vein  from  the  air  bladder.  Note  the 
exact  arrangement  of  these  veins ;  also  the  branching  of  the 
portal  vein  on  the  hinder  surface  of  the  liver. 

Exercise  17.  Draw  a  semidiagrammatic  view  of  the  portal  system. 

The  heart  and  the  pericardial  space.  Cut  away  all  the  muscles 
between  the  gills,  being  very  careful  not  to  injure  the  heart  or 


50  VEETEBEATE  ZOOLOGY 

the  artery  which  issues  from  its  forward  end;  the  pericardial 
cavity  will  be  thus  exposed. 

The  heart  in  fishes  stands  in  close  relation  to  the  gills,  and 
lies  in  the  postero-ventral  portion  of  the  head  between  them. 
It  is  made  up,  as  we  have  seen,  of  three  parts,  the  large  mus- 
cular ventricle,  the  deep  red  auricle,  and  the  sinus  venosus,  the  vessel 
which  lies  across  the  hinder  end  of  the  pericardial  space.  Blood 
is  brought  from  the  various  tissues  to  the  sinus  venosus  by  the 
veins,  from  which  it  flows  into  the  auricle,  and  from  it  into  the 
ventricle. 

The  ventricle  sends  the  blood  forward  into  the  bulbus  arte- 
riosus,  —  a  thick- walled  vessel  in  front  of  the  ventricle,  which  is 
the  beginning  of  the  aorta.  The  muscular  walls  of  the  bulbus 
are  highly  elastic,  and  when  they  are  distended  they  exert  a 
constant  pressure  upon  the  blood  which  is  passing  through  it ; 
the  blood  thus  flows  forward  in  a  constant  stream  and  without 
pulse  beats. 

Exercise  18.  Draw  a  semidiagrammatic  view  of  the  pericardial 
cavity  with  the  heart  and  the  bulbus  arteriosus. 

The  inner  structure  of  the  heart.  Cut  open  the  ventricle  and 
the  bulbus  arteriosus  by  a  lateral  incision  carried  along  the  left 
side  of  both.  Turn  the  flap,  which  consists  of  the  entire  ventral 
wall  of  the  ventricle  and  bulbus,  to  the  right,  and  expose  their 
interior.  Note  the  thick  walls  of  the  ventricle  and  the  small 
cavity  in  the  center ;  in  its  dorsal  wall  is  the  auriculo-ventricular 
opening  into  the  auricle,  —  a  slit  guarded  on  each  side  by  a  valve. 
Use  the  blowpipe  to  bring  this  opening  into  view.  Note  also 
the  thick  walls  of  the  bulbus ;  find  by  using  the  blowpipe,  at 
the  opening  of  the  ventricle  into  the  bulbus,  the  two  valves 
which  prevent  the  blood  from  flowing  backward.  Open  the 
auricle  by  a  lateral  incision ;  blow  into  it  and  note  its  thin  walls 
and  large  cavity.  Find  the  opening  into  the  sinus  venosus, 
which  is  guarded  by  a  single  valve. 

Exercise  19.  Draw  a  diagram  of  the  heart,  showing  the  structure 
of  its  interior. 


THE  PERCH  51 

The  arterial  system.1  The  forward  continuation  of  the  bulbus 
arteriosus  forms  the  aorta  ascendens,  or  ventral  aorta.  This  vessel 
sends  off  four  pairs  of  afferent  branchial  arteries  which  carry  blood 
to  the  gills  :  four  pairs  of  efferent  branchial  arteries  then  run  from 
the  gill  arches  dorsally  to  the  median  plane  where  they  form  the 
aorta  descendens,  or  dorsal  aorta. 

Springing  from  the  dorsal  end  of  the  first  (anterior)  efferent 
branchial  artery,  on  each  side,  is  the  large  carotid  artery,  which 
supplies  the  head;  it  soon  divides  into  two  branches  which 
pass  above  and  below  the  eye.  The  dorsal  aorta  passes  along 
the  dorsal  side  of  the  body  cavity,  just  beneath  the  spinal 
column,  to  the  posterior  end  of  the  body ;  in  the  caudal  region 
it  becomes  the  caudal  artery  and  lies  in  the  ventral  arches  of  the 
vertebra).  It  gives  off  the  paired  spinal  arteries  along  its  entire 
course;  the  cceliac  artery,  a  large  median  vessel  which  leaves  the 
aorta  a  short  distance  back  of  the  branchial  arteries,  and,  break- 
ing up  into  a  number  of  branches,  supplies  the  digestive  tract, 
air  bladder,  and  genital  glands;  and  the  two  subclavian  arteries, 
which  leave  the  aorta  just  back  of  the  cceliac  artery  and  go  to 
the  pectoral  fins. 

First  study  the  ventral  aorta  and  the  afferent  branchial 
arteries.  Entirely  remove  the  lower  jaw  and  the  left  oper- 
culum,  but  do  not  disturb  the  gill  arches ;  with  scissors  cut 
off  the  gills  from  the  arches.  Follow  the  ventral  aorta  from 
the  bulbus  arteriosus  forward  between  the  ventral  ends  of  the 
gill  arches.  Find  the  points  where  the  four  afferent  arteries 
on  the  left  side  leave  the  aorta,  and  trace  the  course  of  each 
along  the  hinder  side  of  the  gill  arches;  the  transparency  of 
the  skin  covering  the  gill  arches  permits  this  to  be  done  easily. 

The  remaining  arteries  will  be  studied  after  the  veins. 

Exercise  20.  Draw  the  arteries  just  observed. 

1  The  aorta  ascendens  and  afferent  branchial  arteries  may  be  injected 
through  the  bulbus  arteriosus.  In  order  to  inject  the  remainder  of  the 
arterial  system,  cut  off  the  tail  a  short  distance  in  front  of  the  caudal  fin 
and  inject  forward  in  the  caudal  artery.  This  is  the  uppermost  of  the  two 
vessels  which  lie  in  the  canal  formed  by  the  bony  arches  on  the  ventral  side 
of  the  spinal  column. 


52  VERTEBKATE  ZOOLOGY 

The  venous  system  (continued).1  The  following  are  the  sys- 
temic veins,  which  carry  blood  directly  to  the  heart.  The  short 
hepatic  vein  enters' the  sinus  venosus  in  the  median  plane.  Press 
the  liver  away  from  the  false  diaphragm  and  find  it.  Joining  each 
end  of  the  transverse  sinus  venosus  is  a  large  and  conspicuous 
duct  or  sinus  called  the  Cuvierian  duct.  The  two  Cuvierian  ducts 
lie  along  the. anterior  end  of  the  abdominal  cavity,  parallel  with 
each  other  and  just  in  front  of  the  liver,  between  the  sinus 
venosus  and  the  head  kidney.  Inasmuch  as  the  head  kidney 
is  dorsal  in  position  and  the  sinus  venosus  ventral,  the  Cuvierian 
ducts  have  an  almost  vertical  position  in  the  body.  Trace  these 
vessels  from  the  sinus  venosus  dorsally :  they  will  be  found  just 
behind  the  posterior  gill  arch.  The  dorsal  ends  of  these  two 
ducts  are  connected  by  a  horizontal  sinus  which  lies  just  beneath 
the  spinal  column. 

Two  pairs  of  prominent  veins  —  the  jugulars  or  anterior  cardinals, 
and  the  posterior  cardinals  —  bring  blood  from  the  anterior  and 
the  posterior  portions  of  the  body,  respectively,  to  the  horizontal 
sinus  of  the  Cuvierian  ducts.  Just  before  joining  the  sinus  the 
two  jugulars  unite  and  form  a  median  vein ;  the  two  posterior 
cardinals  also  unite  and  form  a  median  vein. 

The  two  posterior  cardinals  are  large  and  prominent  veins  and 
lie  just  beneath  the  vertebral  column,  partly  imbedded  in  the 
kidneys ;  the  dorsal  aorta  lies  between  them.  The  left  cardinal 
is  much  larger  than  the  right,  and  much  longer,  and  begins  its 
course  at  the  posterior  end  of  the  body  as  the  caudal  vein ;  this 
vein  lies  in  the  ventral  arches  of  the  spinal  column  and  receives 
the  paired  spinal  veins. 

In  the  trunk  region  it  receives  the  left  spinal  and  renal  veins. 
The  right  cardinal  begins  its  course  in  the  hinder  part  of  the  body 
cavity  and  receives  the  right  spinal  and  renal  veins.  Find  the 
cardinals  in  the  mass  of  the  kidneys  and  trace  them  forward  to 
the  median  cardinal  and  the  Cuvierian  ducts. 

1  The  veins  are  easily  studied  without  injection,  as  the  death  of  the  animal 
leaves  them  filled  with  blood.  If  it  is  wished  to  inject  them,  however,  this  may 
be  done  through  the  caudal  vein,  which  is  the  lowermost  of  the  two  vessels  in 
the  ventral  canal  of  the  vertebral  column. 


THE  PEKCH  53 

Find  the  median  jugular  vein  and  trace  it  and  the  two  jugu- 
lars and  their  branches  as  far  as  possible. 

Entering  the  horizontal  sinus  are  three  additional  veins.  Two 
of  these  are  the  small  paired  subclavian  veins,  which  bring  blood 
from  the  pectoral  fins ;  the  third  is  the  intestinal  vein,  which 
brings  blood  from  the  stomach,  intestine,  and  genital  organs. 
Follow  the  course  of  these  veins  and  their  branches. 

Exercise  21.  Draw  a  diagram  of  the  venous  system,  so  far  as 
observed. 

The  arterial  system  (continued).  We  shall  now  study  the 
efferent  branchial  arteries  and  the  dorsal  aorta  and  its  branches. 
The  afferent  arteries  have  already  been  seen ;  the  efferent  arte- 
ries lie  immediately  posterior  to  them  on  the  gill  arches.  Make 
a  cross  section  of  a  gill  arch  and  note  these  two  arteries ;  the 
afferent  is  the  larger  of  the  two.  Remove  the  ventral  wall  of 
the  pharynx  and  the  heart.  Dissect  away  the  mucous  mem- 
brane which  covers  the  roof  of  the  mouth  and  pharynx.  Trace 
the  efferent  arteries  dorsally  to  the  dorsal  aorta.  Follow  the 
aorta  and  the  arteries  which  branch  from  it,  as  already  explained 
(see  p.  51). 

Exercise  22.  Draw  a  diagram  showing  the  efferent  branchial 
arteries,  the  dorsal  aorta  and  its  branches,  so  far  as  ob- 
served. Carefully  label  all. 

Exercise  23.  Draw  a  diagram  of  the  entire  vascular  system. 

The  body  muscles.  Skin  the  side  of  the  body.  Note  the  great 
muscle  which  forms  the  entire  side  and  extends  from  the  head 
to  the  caudal  fin.  This  complex  muscle  is  made  up  of  a  suc- 
cession of  muscle  segments  called  myotomes  or  myomeres,  which 
are  separated  from  one  another  by  connective-tissue  septa  called 
myocommas.  Each  myotome  is  a  plate,  or  lamella,  between  two 
myocommas,  and  consists  of  parallel  fibers  which  run  across 
from  one  myocomma  to  the  other.  The  fibers  thus  are  not  bound 
together  by  fasciae  as  in  the  muscles  of  the  higher  vertebrates. 
Note  the  zigzag  shape  of  the  edge  of  the  myotome,  which  appears 


54  VERTEBRATE  ZOOLOGY 

on  the  surface  of  the  body ;  note  also  that  each  myotome  may  be 
divided  into  a  dorsal  and  a  ventral  half. 

Exercise  24.  Make  an  outline  of  the  fish  and  draw  in  it  a  few  of 
the  myotomes  and  myocommas. 

Cut  the  tail  off  an  inch  or  two  behind  the  anus  and  study  the 
cut  surface.  The  myotomes  appear  here  in  groups  of  concentric 
circles.  This  appearance  is  due  partly  to  the  fact  that  the  inner 
edge  of  each  myotome,  which  is  attached  to  the  spinal  column 
and  to  its  dorsal  and  ventral  processes,  is  much  anterior  in  posi- 
tion to  the  outer  edge  which  appears  on  the  surface,  and  also 
partly  to  the  zigzag  shape  of  the  myotomes.  Cut  horizontal  and 
dorso ventral  sections  of  the  muscles  and  prove  this. 

Observe  the  other  structures  in  the  cross  section,  —  the  skin 
with  the  scales  and  the  lateral  line,  and  the  spinal  column  with 
the  neural  arch  on  its  dorsal  side  and  the  haemal  arch  on  its 
ventral  side,  the  former  containing  the  spinal  cord  and  the  latter 
the  caudal  artery  and  vein. 

Exercise  25.  Draw  the  cross  section. 

The  skeletal  system.  The  skeleton  of  the  fish  is  made  up  of 
two  distinct  portions,  —  the  exoskeleton  and  the  endoskeleton.  The 
former  is  of  dermal  origin  and  consists  of  the  ctenoid  scales  and 
the  teeth.  The  scales,  are  imbedded  in  the  dermis,  or  inner  layer 
of  the  skin ;  covering  them  on  the  outside  is  a  thin  layer  of  the 
dermis  and  all  the  epidermis,  which,  however,  are  often  broken 
through  by  the  sharp  posterior  tips  of  the  scales.  Of  dermal 
origin  are  also  the  membrane  bones  which  take  part  in  the 
formation  of  the  skull.  These  are,  however,  so  intimately  asso- 
ciated with  the  other  bones  of  the  skull,  which  belong  to  the 
endoskeleton,  that  they  will  be  studied  with  them. 

Pull  out  several  scales,  including  some  from  the  lateral  line, 
and  study  them  with  the  aid  of  a  lens  or  microscope.  Note  the 
parallel  lines  of  growth.  In  the  scales  from  the  lateral  line 
note  the  minute  canal  on  the  inner  side  of  the  scale  and  the 
pore  by  which  it  communicates  with  the  outside. 

Exercise  26.   Make  a  sketch  of  a  scale  from  the  lateral  line. 


THE  PERCH  55 

The  endoskeleton  forms  the  bony  and  cartilaginous  framework 
of  the  body.  It  may  be  divided  into  (1)  the  axial  skeleton,  which 
includes  the  skull  and  the  vertebral  column,  with  the  ribs ;  and 
(2)  the  appendicular  skeleton,  which  includes  the  skeleton  of  the 
paired  and  the  median  fins. 

To*  prepare  the  endoskeleton  for  study  remove  all  the  viscera; 
immerse  the  animal  in  hot  water  in  order  to  soften  the  muscles, 
and  then  carefully  remove  them  from  the  skeleton.  Separate 
the  bones  from  one  another  as  little  as  possible  at  first,  but 
leave  enough  of  the  ligaments  to  bind  them  together.  Be  very 
careful  not  to  remove  any  of  the  bones  of  the  head,  some  of 
which  are  small  and  easily  lost.  If  any  of  the  bones  are  removed 
from  the  skeleton  in  preparation,  they  must  be  carefully  pre- 
served. It  is  of  great  practical  use  to  have  a  dried  skeleton  at 
hand  for  comparison  during  the  dissection.  It  is  not  necessary 
that  this  skeleton  be  thoroughly  cleaned  and  mounted,  but 
any  skeleton  that  has  been  dried  after  the  muscles  have  been 
removed  will  answer  the  purpose. 

The  axial  skeleton;  the  vertebral  column  and  the  ribs.  The 
vertebral  column  consists  of  a  succession  of  bony  vertebrse 
closely  connected  by  intervertebral  ligaments.  They  are  deeply 
biconcave  or  amphicoelous ;  the  two  concavities  are  joined  by 
a  central  canal  and  all  these  spaces  are  filled  with  the  jellylike 
notochord.  The  notochord  thus  forms  a  continuous  structure 
which  runs  the  length  of  the  vertebral  column. 

The  vertebral  column  may  be  divided  into  two  regions,  — 
the  trunk  region,  in  which  ribs  are  present,  and  the  caudal  region, 
in  which  they  are  absent.  Each  trunk  vertebra  is  composed  of  a 
biconcave  body  or  centrum,  from  the  dorsal  side  of  which  arises 
the  neural  arch,  and  from  the  ventrolateral  side  projects  a  pair 
of  long  haemal  processes.  The  neural  arch  is  composed  of  a  pair 
of  neural  processes  and  a  long  median  neural  spine  ;  it  incloses 
the  spinal  cord.  Projecting  from  the  lower  part  of  the  ante- 
rior edges  of  the  neural  processes  is  a  pair  of  small  articular 
processes  called  the  prezygapophyses ;  they  articulate  with  a  pair 
of  projections  from  the  posterior  end  of  the  centrum  of  the 
next  vertebra  called  the  postzygapophyses. 


56  VEETEBEATE  ZOOLOGY 

The  ribs  are  long,  slender  bones  which  project  from  the 
haemal  processes.  The  first  four  or  five  vertebrae  have  no  hae- 
mal processes  and  the  ribs  project  from  their  centra.  The  ribs 
of  teleosts  are  not  homologous  to  those  of  the  higher  verte- 
brates, but  represent  the  distal  ends  of  the  haemal  processes. 
Extending  from  the  ribs  is  also  a  series  of  long,  slender  bones 
which  lie  in  the  myocommas  and  may  be  homologous  to  the 
ribs  of  the  higher  vertebrates ;  they  are  called  intermuscular  bones. 

The  caudal  vertebrae  differ  from  the  others  in  that  the  haemal 
processes  meet  in  the  midveritral  plane  and  fuse,  forming  a 
haemal  spine  and  inclosing  a  space — the  haemal  canal — in  which 
lie  the  caudal  vein  and  artery ;  they  also  do  not  bear  ribs. 

Count  the  trunk  and  caudal  vertebrae.  Note  how  the  for- 
mer grade  into  the  latter.  The  spinal  column  ends  posteriorly 
with  a  fan-shaped  bone  called  the  urostyle,  which  supports  the 
caudal  fin. 

Exercise  27.  Draw  a  posterior  and  also  a  side  view  of  one  of 
the  trunk  vertebrae  ;  draw  the  same  views  of  a  caudal 
vertebra. 

Make  a  sagittal  section  of  a  vertebra.  Examine  the  con- 
cavities with  the  aid  of  a  lens  and  note  the  lines  of  growth. 
The  centrum  increases  in  size  by  the  addition  of  successive 
layers  of  bone  to  the  outside,  each  of  which  is  a  little  larger 
than  the  previous  one  and  hence  overlaps  it;  the  biconcave 
shape  is  the  result  of  this  method  of  growth. 

Exercise  28.  Draw  the  section  on  a  large  scale,  showing  these 
features. 

The  skull.  The  skull  is  composed  of  two  portions,  —  the 
cranium,  which  protects  the  brain  and  the  special  sense  organs, 
and  the  visceral  skeleton,  which  surrounds  the  anterior  end  of  the 
alimentary  canal  and  consists  of  the  framework  of  the  jaws  and 
gill  arches.  These  two  portions  of  the  skull  have  had  a  very 
different  origin  and  are  different  in  character  and  appearance. 
The  cranium  forms  the  entire  dorsal  half  of  the  skull,  and  its 


THE  PERCH  57 

constituent  bones  and  cartilages  are  for  the  most  part  immov- 
ably knit  together,  so  that  they  form  a  single  compact  whole. 
The  visceral  skeleton  forms  the  ventral  half  of  the  skull,  and 
its  bones  and  cartilages  are  mostly  loosely  joined  with  one 
another  and  with  the  cranium. 

The  visceral  skeleton.  Without  at  first  removing  any  of  its 
parts  we  shall  now  study  the  skeleton  of  the  jaws  and  the  gill 
arches.  The  visceral  skeleton  is  made  up  of  a  series  of  seven 
arches  called  the  visceral  arches,  which  surround  the  mouth  and 
pharynx.  In  the  embryonic  teleost,  as  in  the  adult  elasmobranch, 
these  arches  are  composed  entirely  of  cartilage.  This  cartilage 
is  for  the  most  part  replaced  by  bone  as  the  young  teleost  becomes 
older,  so  that  the  visceral  arches  become  bony  structures.  Other 
bones  also  make  their  appearance  in  connection  with  them  which 
do  not  develop  in  the  cartilage  but  in  the  skin  and  in  connective- 
tissue  membranes  covering  the  skull,  and  are  called  membrane 
bones.  Thus,  as  to  the  method  of  origin,  two  kinds  of  bone  are 
present  in  the  skull,  cartilage  bones  and  membrane  bones. 

Each  visceral  arch  is  a  paired  structure  consisting,  of  a  right 
and  a  left  side  which  meet  in  the  midventral  plane.  Each  side 
is  also  made  up  of  several  segments  which  fall  approximately 
into  a  dorsal  and  a  ventral  half. 

The  visceral  arches  may  be  divided  into  two  groups,  —  an  ante- 
rior group,  consisting  of  the  first  two  arches,  which,  with  certain 
membrane  bones,  form  the  skeleton  of  the  jaws,  the  tongue, 
and  the  operculum ;  and  a  posterior  group,  consisting  of  the  last 
five  arches,  which  support  the  gills  and  are  called  the  gill  or 
branchial  arches*  Identify  these  two  groups. 

We  shall  first  study  the  anterior  group.  The  first  visceral 
arch  is  the  mandibular  arch.  The  dorsal  and  ventral  halves  of  it, 
together  with  certain  membrane  bones,  form  the  skeleton  of  the 
upper  jaw,  the  roof  of  the  mouth,  and  the  lower  jaw.  The 
second  visceral  arch  is  the  hyoid  arch,  the  dorsal  half  of  which 
enters  into  relation  with  the  mandibular  arch  and  becomes  the 
suspensorium  of  the  jaws,  i.e.  the  connecting  link  between  them 
and  the  cranium,  while  the  ventral  half  forms  the  support  of  the 
tongue  and  bears  the  opercular  bones  and  the  branchiostegal  rays. 


58  VEKTEBEATE  ZOOLOGY 

The  mandibular  arch.  Identify  the  following  bones  forming 
the  lower  jaw,  the  ventral  half  of  this  arch.  At  its  proximal 
end  is  the  large  articular  bone,  by  means  of  which  it  articu- 
lates with  the  quadrate  bone  of  the  upper  jaw.  This  is  a  carti- 
lage bone,  being  an  ossification  of  the  posterior  end  of  Meckel's 
cartilage.  In  the  elasmobranch  Meckel's  cartilages  form  the 
lower  jaw.  In  the  teleost  they  are  also  present,  forming  the 
axis  of  the  lower  jaw,  their  posterior  ends  only  having  ossified. 
The  forward  and  middle  surfaces  of  the  lower  jaw  are  formed 
on  each  side  .by  the  large  dentary  bone,  which  bears  teeth.  This 
is  a  membrane  bone,  having  formed  around  Meckel's  cartilage, 
which  is  visible  in  a  groove  on  its  inner  surface  in  a  fresh 
skull.  A  small  additional  membrane  bone  —  the  angular  —  is 
present  at  the  hinder  end  of  the  jaw. 

Identify  the  bones  of  the  upper  jaw.  Forming  the  forward 
end  and  the  lateral  margins  of  this  jaw  are  two  pairs  of  mem- 
brane bones,  —  the  premaxillae  and  the  maxillae.  The  former  bear 
teeth  and  meet  each  other  in  the  middle  line  in  front ;  the 
latter  are  without  teeth,  being  a  pair  of  flattened  rods  back  of 
the  premaxillse,  with  which  their  anterior  ends  articulate. 

The  hinder  end  of  the  upper  jaw  is  made  up  of  a  series  of 
paired  bones  which  have  ossified  in  or  around  the  pterygo- 
quadrate  cartilage,  which  forms  the  embryonic  upper  jaw  of 
the  teleost  and  the  adult  upper  jaw  of  elasmobranchs.  The 
quadrate  bone  is  a  large  triangular  bone  at  the  hinder  end  of  the 
upper  jaw  on  each  side,  with  which  the  lower  jaw  articulates. 
The  metapterygoid  is  a  large  bone  lying  just  above  the  quadrate 
and  back  of  the  orbit.  The  ectopterygoid  is  an  elongated  bone 
which  projects  in  front  of  the  quadrate.  The  endopterygoid  is  a 
thin  plate  above  the  anterior  end  of 'the  ectopterygoid  and  form- 
ing a  part  of  the  roof  of  the  mouth.  In  front  of  the  last  two 
bones  is  the  palatine,  which  helps  form  the  roof  of  the  mouth 
and  bears  teeth. 

Of  these  bones  the  quadrate  and  the  pterygoids  are  ossi- 
fications of  the  pterygoquadrate  cartilage ;  the  palatine  is  a 
membrane  bone  which  forms  around  the  anterior  end  of  this 
cartilage. 


THE  PERCH  59 

Surrounding  the  orbit  and  forming  its  margin  on  all  except 
the  dorsal  side  is  a  row  of  membrane  bones  called  the  suborbitals, 
which  are  very  easily  lost  in  the  cleaning.  The  most  anterior 
one  is  a  large  bone  between  the  orbit  and  the  maxilla,  on  the 
surface  of  which  will  be  seen  radiating  canals  belonging  to  the 
lateral-line  system  of  sensory  canals. 

The  hyoid  arch.  The  dorsal  half  of  this  arch  forms  the  sus- 
pensorium.  It  is  formed  by  the  hyomandibular  and  the  symplectic 
bones.  The  former  is  a  large  bone  which  extends  from  the  cra- 
nium veiitrally,  back  of  the  metapterygoid  to  the  symplectic; 
the  latter  is  a  small  bone  which  lies  just  dorsal  to  the  hinder 
end  of  the  quadrate  ;  the  jaws  are  thus  joined  with  the  cranium. 

The  ventral  half  of  the  arch  is  formed  by  a  row  of  bones,  on 
each  side,  which  extend  ventrally  from  the  junction  of  the  sym- 
plectic and  the  hyomandibular  and  are  called  collectively  the 
hyoid  bones.  These  are  the  interhyal,  epihyal,  ceratohyal,  and  the 
two  hypohyal  bones ;  of  which  the  epihyal  and  ceratohyal  are 
the  largest  and  bear  the  branchiostegal  rays.  In  the  middle 
area  between  the  right  and  left  sides  of  the  hyoid  arch  is  the 
basihyal  bone,  which  supports  the  tongue. 

Articulating  with  both  the  dorsal  and  ventral  halves  of  the 
hyoid  arch  on  each  side  are  bony  plates  and  rods  which  support 
structures  guarding  the  openings  of  the  gill  slits :  these  are  the 
opercular  bones  and  the  branchiostegal  rays.  There  are  four  oper- 
cular  bones :  the  preopercular  lies  along  and  back  of  the  hyoman- 
dibular and  symplectic  bones  ;  the  opercular  is  a  broad  bone  just 
back  of  the  preopercular  and  the  hyomandibular,  the  hinder 
border  of  which  is  drawn  out  into  a  long  spine  ;  the  interopercular 
and  subopercular  lie  along  the  ventral  borders  of  the  preopercular 
and  the  opercular  respectively. 

Articulating  with  the  ventral  half  of  the  hyoid  arch  are  seven 
slender  arched  bones,  the  branchiostegal  rays,  which  support  the 
branchiostegal  membrane.  Note  with  which  bones  they  articulate. 

Exercise  29.  Draw  a  semidiagrammatic  view  of  the  side  of  the 
skull  on  a  scale  of  2,  and  carefully  label  all  the  bones  just 
mentioned. 


60  VEETEBEATE  ZOOLOGY 

Remove  the  opercular  bones  and  the  lower  jaw.  Remove 
the  suborbital  bones.  The  lateral  aspect  of  the  gill  arches,  the 
hyoid  bones  with  the  branchiostegal  rays,  the  hyomandibular, 
symplectic,  and  the  pterygoids  will  be  seen.  Carefully  clean 
them  with  a  brush  but  do  not  remove  them. 

Exercise  so.  Draw  this  aspect,  showing  these  bones. 

Disarticulate  and  remove  the  five  gill  arches  and  the  hyoid 
arch  from  the  body.  In  the  midventral  area  and  joining  these 
arches  is  a  row  of  median  bones  called  the  basibranchials,  or 
copulae;  the  copula  of  the  hyoid  arch  is  the  basihyal,  which  sup- 
ports the  tongue  and  has  already  been  described.  The  first, 
second,  and  third  gill  arches  each  articulates  with  its  median 
basibranchial  by  means  of  a  short  bone  called  the  hypobranchial. 
The  next  bone  in  each  arch  is  the  largest  and  forms  the  main 
part  of  it ;  it  is  called  the  ceratobranchial.  The  fourth  arch  artic- 
ulates by  its  ceratobranchial  with  the  basibranchial;  the  fifth 
arch  consists  of  a  ceratobranchial  alone  and  bears  teeth. 

The  next  bone  dorsally  in  all  except  the  fifth  arch  is  the 
epibranchial.  This  is  followed  by  the  pharyngobranchial,  which  joins 
its  fellow  of  the  opposite  side  in  the  middorsal  line.  In  the 
second,  third,  and  fourth  arches  the  pharyngobranchials  are 
broad  plates  which  bear  teeth  ;  in  the  first  arch  the  pharyn- 
gobranchial is  a  small  bone  which  joins  that  arch  with  the 
cranium.  Note  which  of  these  bones  bear  gill  rays. 

Exercise  31.  Make  a  drawing  of  the  ventral  aspect  of  the  gill 
and  hyoid  arches  on  a  scale  of  2;  carefully  label  their 
various  parts. 

Exercise  32.  Make  a  drawing  of  the  roof  of  the  mouth  and  care- 
fully label  all  the  bones  already  studied. 

Remove  the  premaxillary,  maxillary,  palatine,  pterygoid, 
quadrate,  symplectic,  and  hyomandibular  bones,  and  study  the 
cranium. 

The  cranium  is  a  complicated  structure,  made  up  of  a  large 
number  of  bones  and  cartilages.  The  bones  are  so  tightly  bound 


THE  PEECH  61 

together  that  the  sutures  are  often  indistinguishable  until  the 
skull  has  been  boiled  or  soaked  a  long  time  in  an  ammonia  solu- 
tion ;  the  cartilages  are  the  remains  of  the  chondrocranium,  the 
primitive  cartilaginous  cranium  which  forms  the  skull  of  the 
young  animal,  and  in  the  adult  fish  is  partly  replaced  by  bone. 
As  in  the  case  of  the  visceral  portion  of  the  skull  the  bones  of 
the  cranium  fall  into  two  categories,  —  the  cartilage  bones,  which 
develop  in  and  replace  the  primitive  cartilage,  and  the  membrane 
bones,  which  develop  independently  of  the  cartilage  in  connect- 
ive-tissue membranes  and  in  the  dermis  of  the  skin. 

Two  distinct  regions  are  present  in  the  cranium:  (a)  the 
cranium  proper,  which  is  the  brain  case  and  comprises  the  bones 
and  cartilages  in  the  medial  portions  of  the  skull ;  and  (b)  the  cap- 
sules of  the  special  sense  organs,  which  protect  the  optic,  auditory, 
and  nasal  organs. 

Observe  the  general  character  of  the  cranium.  Note  the  small 
brain  cavity  and  the  foramen  magnum,  the  opening  at  the  hinder 
end  of  the  cranium  by  which  the  spinal  cord  enters  it.  Note  the 
orbit,  which  occupies  a  large  space  on  the  side  of  the  cranium ; 
the  portion  of  the  cranium  in  front  of  it  forms  the  nasal  capsule ; 
that  back  of  it  on  each  side  is  the  auditory  capsule.  Note  the 
two  flat  spines  which  project  back  of  the  auditory  capsule  on 
each  side. 

Study  the  posterior  aspect  of  the  cranium.  The  hinder  end 
is  formed  of  four  occipital  bones,  all  of  which  are  cartilage  bones. 
The  basioccipital  is  ventral ;  its  concave  posterior  surface  articu- 
lates with  the  centrum  of  the  first  vertebra.  The  two  exoccipitals 
inclose  the  foramen  magnum  between  themselves;  each  bears 
a  broad  articular  surface  which  meets  a  corresponding  one  on 
the  neural  arch  of  the  first  vertebra.  The  foramen  of  the  vagus 
nerve  is  in  the  exoccipital  on  each  side.  The  supraoccipital  is 
dorsal  and  bears  a  broad  median  spine.  On  each  side  of  these 
bones  and  forming  the  postero-lateral  part  of  the  cranium  is  the 
auditory  capsule. 

Exercise  33.  Draw  the  hinder  end  of  the  skull  on  a  scale  of  2, 
showing  outlines  of  these  bones. 


62  VERTEBRATE  ZOOLOGY 

Study  the  dorsal  .aspect  of  the  cranium.  Extending  in  front 
of  the  supraoccipital  are  the  two  large  frontal  bones;  these  are 
membrane  bones  which  form  the  greater  part  of  the  roof  of  the 
skull  and  the  medial  walls  of  the  orbits.  Immediately  back  of 
the  frontal  bone  on  each  side  is  the  small,  irregular  parietal,  also 
a  membrane  bone. 

The  auditory  capsule  is  formed  of  an  intricate  complex  of  bones 
at  the  postero-lateral  corner  of  the  skull.  From  the  hinder  end 
of  the  capsule  two  prominent  spinelike  processes  project,  these 
processes  on  the  two  sides,  together  with  the  median  supra- 
occipital  spine,  forming  the  five  prominent  projections  at  the 
hinder  end  of  the  skull. 

Of  the  two  lateral  processes  the  more  dorsal  is  the  epiotic 
process ;  it  is  formed  by  the  small  epiotic  bone,  which  lies  lateral 
to  the  supraoccipital  and  behind  the  parietal.  The  more  ventral 
process  is  the  parotic  process.  It  is  formed  by  two  bones,  —  the 
more  dorsal  being  the  pterotic,  the  more  ventral  the  opisthotic,  — 
the  latter  of  which  contains  the  foramen  of  the  glossopharyn- 
geal  nerve.  Directly  in  front  of  the  opisthotic  is  the  probtic 
bone,  through  the  anterior  border  of  which  go  the  trigeminal  arid 
facial  nerves,  and  directly  above  which  is  the  sphenotic.  These 
five  otic  bones  are  all  cartilage  bones  which  form  the  auditory 
capsule. 

Just  in  front  of  the  prootic  and  sphenotic  are  two  cartilage 
bones,  —  the  orbitosphenoid  and  the  alisphenoid, —  the  former  being 
the  more  ventral  of  the  two ;  they  belong  to  the  cranium  proper, 
lying  in  the  lateral  wall  of  the  brain  case,  and  are  not  seen  from 
above. 

In  front  of  the  frontals  and  forming  the  anterior  end  of  the 
cranium  are  the  paired  nasals,  which  form  the  roof  of  the  nasal 
capsule. 

Exercise  34.  Draw  the  dorsal  aspect  of  the  cranium  on  a  scale 

of  2. 

Study  the  ventral  aspect.  Three  bones  form  the  medial  por- 
tion of  the  ventral  wall  of  the  cranium,  —  the  basioccipital  at  the 
hinder  end,  the  vomer  at  the  forward  end,  and  the  long  slender 


THE  PEKCH  63 

parasphenoid  or  parabasal  between.  The  latter  two  are  membrane 
bones ;  the  vomer  bears  teeth  and  forms  the  ventral  wall  of  the 
nasal  capsule. 

In  front  of  the  orbits  and  directly  above  the  vomer  are  the 
median  ethmoid  and  the  two  lateral  ethmoids,  which  are  cartilage 
bones  forming  the  anterior  end  of  the  cranium  proper  and  the 
hinder  end  of  the  nasal  capsules. 

The  cranium,  as  we  have  already  seen,  is  composed  of  the 
cranium  proper  and  the  special  sense  capsules.  The  former, 
which  is  the  brain  case,  contains  the  following  bones :  the  occip- 
itals,  parietals,  frontals,  sphenoids,  ethmoids,  and  parabasal. 
The  sense  capsules  inclose  the  auditory,  optic,  and  olfactory 
organs.  The  auditory  capsule  is  made  up  of  the  otic  bones. 
The  optic  capsule  does  not  ossify,  but  remains  largely  mem- 
branous; the  sclera  of  the  eyeball,  however,  contains  carti- 
lage, and  certain  membrane  bones  —  the  suborbitals  —  appear 
around  the  orbit.  The  nasal  capsule  contains  the  nasals  and  the 
vomer;  the  ethmoids  also  enter  into  relations  with  the  hinder 
part  of  it. 

Exercise  35.  Draw  the  ventral  aspect  of  the  cranium  on  a  scale 
of  2,  showing  outlines  of  the  bones. 

Exercise  36.  Draw  the  lateral  aspect. 

Boil  the  cranium  until  the  bones  can  be  separated  from  one 
another,  and  study  them  carefully. 

The  appendicular  skeleton.  Four  median  fins  are  present,  —  an 
anterior  and  a  posterior  dorsal  fin,  a  ventral  fin,  and  a  caudal  fin. 
The  framework  of  the  two  dorsal  fins  and  that  of.  the  ventral 
fin  are  essentially  alike ;  each  consists  of  a  series  of  elongated 
bones,  the  basals  and  radials.  The  former  are  long,  flattened  plates 
which  lie  imbedded  between  the  muscles  of  the  right  and  left 
sides  of  the  body,  alternating  with  the  haemal  and  neural  spines. 
Articulating  with  the  outer  end  of  each  of  these  bones  is  a  radial, 
or  fin  ray,  a  straight  bony  rod.  Note  the  two  kinds  of  fin  rays, 
the  sharp  stiff  ones,  and  the  jointed  flexible  ones.  The  anterior 
basal  does  not  bear  a  radial.  The  caudal  fin  is  without  basals, 


64  VEKTEBEATE  ZOOLOGY 

the  radials  joining  directly  with  the  urostyle  and  the  neural 
and  haemal  spines. 

Exercise  37.  Draw  the  skeleton  of  a  dorsal  fin  and  that  of  the 
caudal  fin. 

The  paired  fins.  The  pectoral  fin  consists  of  about  fifteen  fin 
rays  and  four  small  basals,  the  latter  articulating  with  the  pec- 
toral girdle.  This  structure  is  formed  of  several  bones,  of  which 
two  —  the  scapula  and  coracoid  —  articulate  with  the  basals,  the 
former  of  these  bones  being  dorsal  to  the  latter.  These  bones 
are  cartilage  bones  and  represent  the  pectoral  girdle  of  the 
elasmobranch.  In  addition  to  these  are  a  number  of  membrane 
bones  which  join  the  fin  with  the  cranium.  The  cleithrum,  or 
so-called  clavicle,  is  the  largest  of  these  and  extends  upward 
from  the  anterior  border  of  the  scapula  and  coracoid.  Its  dorsal 
end  joins  the  supracleithrum,  which  in  turn  is  joined  with  the 
skull  by  the  V-shaped  posttemporal. 

Exercise  38.  Draw  the  pectoral  fin  and  girdle. 

The  pelvic  fins.  Each  of  these  consists  of  about  five  radials. 
At  their  proximal  ends  they  articulate  with  a  large  plate  which 
represents  the  fused  basals.  These  two  plates  lie  alongside  of 
each  other  in  the  median  area ;  no  pelvic  girdle  is  present. 

Exercise  39.  Draw  the  pelvic  fins. 


CHAPTER  II 

AMPHIBIANS 
A  URODELAN  AMPHIBIAN.    NECTURUS 

Necturus,  or  the  mud  puppy,  is  one  of  the  largest  of  the  sali- 
manders.  It  is  common  throughout  the  central  portions  of  the 
country,  where  it  lives  in  lakes  and  streams  upon  small  fishes  and 
other  animals.  It  is  one  of  the  most  primitive  of  the  urodeles. 
The  external  gills  —  which  in  most  amphibians  are  larval  char- 
acters and  disappear  as  the  animal  becomes  adult  —  are  retained 
throughout  life  by  Necturus ;  it  never  leaves  the  water. 

Three  specimens  will  be  needed  for  a  complete  dissection,  — 
one  for  the  study  of  the  external  characters  and  the  viscera, 
including  the  heart  and  the  principal  blood  vessels ;  one  for 
the  dissection  of  the  entire  vascular  system;  and  one  for  the 
skeleton.  A  five  per  cent  solution  of  formalin  should  be  used 
to  preserve  them  in. 

Place  the  animal,  alive  if  possible,  on  a  dissecting  board  or  in 
a  large  pan  and  observe  its  form  and  color.  The  body  is  cylin- 
drical in  shape,  flattened  dorsoventrally  except  at  the  hinder 
end,  which  is  compressed  laterally  and  surrounded  by  a  dorso- 
ventral  fin.  The  tail  is  the  principal  organ  of  locomotion.  The 
small,  weak  legs,  with  the  clawless  toes,  are  only  of  use  when 
the  animal  walks ;  while  it  is  swimming  they  are  held  against 
the  sides  of  the  body. 

The  skin  of  Necturus  is  smooth,  as  in  most  amphibians,  and 
without  bony  or  horny  scales  or  other  hardened  integumentary 
structures,  such  as  are  possessed  by  all  the  other  groups  of  ver- 
tebrates. It  is,  however,  provided  with  numerous  integumen- 
tary glands  which  secrete  a  protective  but  nonpoisonous  slime. 
Along  the  middle  of  the  back  a  double  row  of  these  glands  will 
be  seen  when  the  skin  is  removed. 

65 


66  VEKTEBEATE   ZOOLOGY 

Note  the  color  of  the  animal  and  the  variation  of  color  on  the 
dorsal  and  ventral  sides.  The  animal  is  well  fitted  by  its  color 
for  a  life  in  the  dimly  lighted  waters  in  which  it  is  found. 

The  body  of  the  animal  may  be  divided  into  three  regions,  — 
the  head,  the  trunk,  and  the  tail.  The  neck  region,  which  is  want- 
ing in  fishes  and  is  so  characteristic  of  land  vertebrates,  is  just 
beginning  to  make  its  appearance  in  amphibians.  A  distinct 
neck  is  wanting,  but  a  cervical  vertebra  is  present  with  which 
the  skull  articulates. 

The  head.  This  body  division  is  bluntly  triangular  in  shape 
and  is  very  flat  and  broad.  The  mouth  is  rather  small  and  the 
lips  are  prominent.  At  the  sides  of  the  mouth  note  how  the 
upper  lip  dovetails  into  a  fold  of  the  lower  lip.  The  two  nostrils 
are  at  the  anterior  end  of  the  head  and  widely  separated  from 
each  other ;  each  can  be  tightly  closed  by  a  fold  of  skin.  The 
eyes  are  small  and  do  not  project.  No  eyelids  are  present;  the 
skin  passes  without  interruption  over  the  eyes,  but  is  transpar- 
ent in  front  of  them.  The  ear,  as  in  fishes,  is  entirely  within 
the  skull,  no  portion  of  it  appearing  on  the  surface.  Integu- 
mental  sense  buds,  such  as  occur  on  the  head  and  in  the  lateral 
line  of  fishes,  are  present  on  the  head  and  body  of  Necturus,  but 
will  hardly  be  seen. 

The  posterior  part  of  the  head  is  marked  by  a  ventral  trans- 
verse fold  of  the  skin  and  also  by  three  pairs  of  gills.  These 
gills  are  not  homologous  to  the  gills  of  fishes,  but  are  projec- 
tions of  the  outer  integument;  note  carefully  their  character 
and  shape.  Between  the  first  and  second  and  the  second  and 
third  gills  on  each  side  is  a  gill  cleft,  a  slitlike  opening  into  the 
pharynx.  Probe  these  clefts.  Necturus  has  a  twofold  method 
of  respiration,  —  by  means  of  lungs,  and  through  the  entire 
outer  surface  of  the  body  and  the  gills.  Inasmuch  as  the 
animal  never  leaves  the  water,  the  latter  method  is  the  more 
important  one. 

The  trunk  and  the  tail  pass  gradually  into  each  other.  They 
are  without  external  segmentation,  but  the  muscle  segments 
can  usually  be  detected  through  the  skin.  The  trunk  bears  the 
appendages.  A  short  distance  back  of  the  hinder  appendages  in 


NECTURUS  67 

the  ventral  surface  is  the  large  anus,  the  opening  of  the  cloaca. 
Note  its  shape ;  its  lips  are  often  swollen  in  consequence  of  the 
absorption  of  water  by  the  cloacal  glands. 

The  appendages.  The  twu  pairs  of  legs  are  nearly  of  the  same 
size  and  are  widely  separated  from  each  other.  Each  leg  is  com- 
posed of  three  divisions,  —  a  proximal,  a  middle,  and  a  distal  division. 
In  the  fore  limb  these  segments  are  the  upper  arm,  the  forearm, 
and  the  wrist  and  hand  respectively ;  in  the  hind  limb  they  are 
the  thigh,  the  shank,  and  the  ankle  and  foot. 

Note  the  position  of  the  limbs  with  reference  to  the  trunk, 
which  in  Necturus  is  of  a  primitive  character.  In  their  most 
primitive  position  the  limbs  of  vertebrates  are  straight,  and 
extend  at  right  angles  to  the  body.  Each  limb  has  in  this  posi- 
tion a  dorsal  and  a  ventral  surface,  and  an  anterior  or  preaxial 
and  a  posterior  or  postaxial  surface.  If  the  human  arm  be  ex- 
tended straight  out  from  the  body  with  the  thumb  up,  it  will 
assume  this  primitive  position ;  the  back  of  the  hand  will  be  dor- 
sal, the  palm  ventral,  and  the  thumb  will  be  preaxial  or  anterior 
in  position. 

The  first  modification  of  this  primitive  position,  which 
occurred  as  a  result  of  locomotion  on  a  hard  surface,  was  the 
bending  of  the  middle  segment  of  the  leg  ventrally  and  the  dis- 
tal segment  more  or  less  dorsally.  The  proximal  segment  retained 
its  primitive  position ;  the  middle  segment  bent  downward ; 
and  the  distal  segment  assumed  more  or  less  its  original  posi- 
tion again,  at  right  angles  to  the  body  but  in  a  different  plane. 
This  is  approximately  the  position  the  limbs  have  in  Necturus ; 
it  enables  the  limbs  to  raise  the  trunk  above  the  ground  and  to 
propel  it  slowly  forward. 

Exercise  i.  Draw  the  dorsal  aspect  of  the  animal. 
Exercise  2.  Draw  the  ventral  aspect. 

Exercise  3.  Draw  a  side  view  of  the  head  on  a  scale  of  2  or  3, 
showing  accurately  the  gills,  eyes,  nostrils,  and  lips. 

The  animal  may  be  killed  by  immersing  it  in  warm  water 
(about  43°  C.  or  110°  Fahr.)  or  by  putting  it  under  a  bell  jar 


68  VERTEBRATE  ZOOLOGY 

with  a  wad  of  cotton  soaked  in  chloroform  or  ether.  While  un- 
der the  influence  of  the  anaesthetic  a  large  quantity  of  slime 
usually  exudes  from  its  skin;  this  slime  must  be  scraped  off. 

The  mouth  and  pharynx.  Cut  back  through  the  angle  of  the 
jaw  on  each  side  until  the  lower  jaw  can  be  laid  back  and  the 
mouth  and  pharynx  fully  exposed. 

The  mouth  and  pharynx  form  a  single  large  cavity,  which 
extends  back  to  the  opening  of  the  oesophagus,  the  pharynx 
being  that  part  of  it  which  contains  the  respiratory  openings, 
i.e.  the  glottis  and  gill  clefts.  Note  the  large  lips ;  also  the  two 
rows  of  teeth  in  the  upper  jaw  and  the  single  row  in  the  lower 
jaw  which  fits  between  them.  In  the  floor  of  the  mouth  is  the 
short  tongue,  supported  by  the  large  cartilaginous  bars  which 
form  the  hyoid  apparatus.  These  bars  can  be  felt  through  the 
mucous  membrane  of  the  mouth.  Just  back  of  this  apparatus 
and  joined  with  it  are  the  gill  arches.  Note  the  gill  clefts  and 
probe  them.  Between  the  gills  in  the  median  line  is  a  small 
longitudinal  slit,  the  glottis,  the  opening  into  the  lungs.  It  is 
bounded  on  the  sides  by  the  delicate  arytenoid  cartilages,  which 
form  the  primitive  larynx.  On  the  roof  of  the  mouth  the  poste- 
rior nares  will  be  found,  between  the  lateral  rows  of  teeth ;  they 
are  a  pair  of  small  openings  which  form  the  communication 
between  the  pharynx  and  the  nasal  capsules.  Probe  them. 

Exercise  4.  Draw  a  sketch  of  the  mouth  and  pharynx,  showing 
both  floor  and  roof. 

The  internal  organs.  Open  the  body  cavity  in  the  following 
way.  Place  the  animal  on  its  back  in  the  dissecting  pan  or  on  a 
dissecting  board,  with  the  head  away  from  you,  and  fasten  it 
there  firmly  by  means  of  a  large  pin  at  each  end  and  one  through 
each  leg.  Then  with  a  sharp  scalpel  and  scissors  make  an  inci- 
sion through  the  body  wall,  a  short  distance  to  one  side  of  the 
median  line,  from  the  hinder  end  of  the  head  to  the  anus,  taking 
care  not  to  cut  too  deeply,  especially  at  the  forward  end  where 
the  heart  and  its  great  vessels  lie  near  the  ventral  surface.  The 
pectoral  girdle  and  also  the  pelvic  girdle  will  be  cut  through 
by  this  incision.  Pull  the  two  flaps  of  the  body  wall  apart,  but 


NECTUEUS  69 

without  cutting  or  disturbing  any  organs  within,  and  examine 
the  viscera  as  they  lie  in  the  body  cavity. 

The  body  cavity  is  divided  into  two  very  unequal  divisions, 
the  larger  and  posterior  of  which  is  the  abdominal  cavity ;  this  is 
lined  by  the  peritoneum,  the  glistening  membrane  on  its  inner 
surface,  and  contains  the  larger  part  of  the  viscera.  The  anterior 
division  is  the  pericardial  cavity ;  it  is  lined  by  the  pericardium  and 
is  very  small,  containing  only  the  heart.  These  two  divisions 
are  separated  by  the  false  diaphragm,  which  is  composed  of  the 
posterior  wall  of  the  pericardium  and  the  anterior  wall  of  the 
peritoneum. 

Note  that  the  organs  in  the  abdominal  cavity  are  attached  to 
its  walls  by  delicate  membranes.  These  are  the  mesenteries, 
which  are  folds  of  the  peritoneum.  This  membrane  forms  a 
closed  sac  lining  the  abdominal  cavity;  the  various  organs  of 
this  cavity  project  into  the  sac  and  are  suspended  in  peritoneal 
folds  which  form  the  mesenteries  and  extend  into  its  interior 
from  its  walls. 

The  most  prominent  organ  in  the  abdominal  cavity  is  the 
liver,  an  elongated,  dark-colored  body  which  is  attached  to  the 
ventral  wall  of  the  cavity  by  a  median,  vertical  mesentery.  At 
the  right  of  it  (the  animal's  left)  is  the  stomach,  which  is  of  about 
the  same  length  as  the  liver,  and  at  the  left  of  the  stomach  is  the 
elongated,  dark-colored  spleen.  Between  the  hinder  end  of  the 
stomach  and  the  liver  will  be  seen  the  cream-colored  pancreas. 
Behind  the  stomach  are  the  coils  of  the  intestine,  attached  to 
the  dorsal  body  wall  by  an  extensive  mesentery.  Between  the 
stomach  and  spleen  and  the  dorsal  body  wall  may  be  seen  the 
narrow,  cylindrical  left  lung.  At  the  posterior  end  of  the  abdom- 
inal cavity  is  the  urinary  bladder,  a  large  sac,  which  may  appear 
large  and  distended  or  very  much  contracted. 

The  heart  and  the  pericardial  cavity.  Carefully  cut  away  the 
body  wall  over  the  heart  and  expose  the  pericardial  cavity. 
The  heart  is  composed  of  five  divisions,  a  single  ventricle,  two 
auricles,  the  sinus  venosus,  and  the  truncus  arteriosus. 

The  ventricle  is  the  conical,  posterior  portion  of  the  heart. 
The  auricles  are  a  pair  of  thin-walled  and  dark-colored  sacs  in 


70  VERTEBBATE  ZOOLOGY 

front  of  the  ventricle ;  they  are  not  completely  separated  from 
each  other.  The  sinus  venosus  is  a  large,  thin-walled  sac  which 
lies  dorsal  to  the  ventricle  and  is  in  communication  with  the 
right  auricle ;  it  will  be  seen  by  turning  the  ventricle  to  one 
side.  The  truncus  arteriosus  is  the  forward  continuation  of  the 
ventricle ;  it  is  composed  of  two  portions,  —  the  conus  arteriosus, 
which  is  immediately  in  front  of  the  ventricle,  and  the  bulbus 
arteriosus,  the  enlarged  anterior  portion  of  the  truncus  which  is 
the  beginning  of  the  ventral  aorta.  The  muscular  walls  of  the 
bulbus  exert  a  steady  pressure  on  the  blood  passing  through  it, 
so  that  the  latter  goes  forward  with  a  steady  flow  instead  of 
by  beats.  .  * 

At  its  anterior  end  the  bulbus  continues  forward  as  the  ventral 
aorta  ;  this  vessel  soon  splits  into  two  pairs  of  arteries  which  carry 
the  blood  to  the  gills ;  the  posterior  pair  goes  to  the  second  and 
third  pairs  of  gills,  and  the  anterior  pair  to  the  first  pair  of  gills. 

Exercise  5.  Draw  an  outline  of  the  animal  and  in  it  outlines  of 
the  internal  organs  as  they  lie  in  the  abdominal  and  peri- 
cardial  cavities  ;  carefully  label  all. 

The  digestive  system.  This  is  composed  of  the  mouth,  phar- 
ynx, oesophagus,  stomach,  small  intestine,  liver,  pancreas,  large 
intestine,  and  cloaca.  • 

Observe  the  great  length  of  the  stomach.  Its  anterior  or  cardiac 
end,  and  the  short  (Esophagus,  which  joins  it  with  the  pharynx, 
are  concealed  by  the  heart.  Cut  out  the  heart.  The  posterior  or 
pyloric  end  of  the  stomach  is  marked  by  a  constriction  and  is 
situated  near  the  posterior  end  of  the  liver. 

The  intestine  extends  from  the  stomach  to  the  cloaca.  Two 
regions  may  be  distinguished,  —  the  small  intestine  and  the  large 
intestine.  The  former  makes  up  the  greater  part  of  the  intes- 
tine; its  anterior  end,  which  may  be  called  the  duodenum,  bends 
forward  so  as  to  lie  parallel  with  the  stomach  for  a  short  dis- 
tance, and  in  the  angle  thus  formed  lies  an  irregularly  folded 
organ,  —  the  pancreas.  The  large  intestine  is  somewhat  thicker 
than  the  small  intestine,  and  joins  it  with  the  cloaca  at  the 
hinder  end  of  the  abdominal  cavity. 


NECTUEUS  71 

Extend  the  intestine  as  much  as  possible  without  cutting 
the  mesentery  which  joins  the  entire  digestive  tract  with  the 
dorsal  body  wall.  Observe  the  numerous  veins  which  lie  in  this 
mesentery;  they  belong  to  the  hepatic  portal  system  and  carry 
blood  from  the  wall  of  the  intestine  to  the  liver.  The  intestinal 
veins  will  be  seen  running  from  the  wall  of  the  intestine  to  the 
large  mesenteric  vein,  —  a  longitudinal  vessel  which  extends  from 
the  hinder  part  of  the  abdominal  cavity  to  the  liver. 

Observe  the  cloaca.  Probe  through  the  anus  into  it.  The  clo- 
aca is  the  common  receptacle  into  which  the  genital  and  urinary 
ducts,  as  well  as  the  intestine,  empty  their  products. 

Study  the  liVer  and  pancreas.  Observe  the  lobes  of  the  liver 
and  the  position  of  the  spherical  gall  bladder  under  the  right 
lobe.  The  bile  duct  joins  the  liver  with  the  intestine;  it  emerges 
from  the  gall  bladder,  receives  a  branch  from  the  liver,  and 
passes  through  the  pancreas  to  the  bend  of  the  duodenum.  By 
squeezing  the  gall  bladder  with  forceps  the  dark-green  bile  can 
often  be  forced  into  the  bile  duct. 

The  pancreas  is  an  elongated  organ  lying  between  the  duo- 
denum and  the  stomach  ;  its  secretion  is  poured  into  the  bile 
duct  through  numerous  fine  canals. 

Partially  imbedded  in  the  dorsal  surface  of  the  liver  will  be 
seen  the  large  postcaval  vein ;  it  runs  along  the  entire  length  of 
the  liver  and  receives  from  it  numerous  small  hepatic  veins.  The 
postcaval  vein  carries  blood  from  the  middle  and  hinder  por- 
tions of  the  body  to  the  heart. 

Exercise  6.  Draw  a  semidiagrammatic  sketch  of  the  digestive 
system,  with  the  liver,  the  pancreas,  and  the  mesentery. 

Cut  the  mesentery  joining  the  lungs  with  the  stomach. 
Remove  the  stomach,  intestine,  liver,  and  pancreas  from  the 
body  ;  leave  the  lungs  in  the  body. 

The  urogenital  system.  The  urinary  and  genital  organs, 
although  very  different  in  function,"  stand  in  close  relation  to 
each  other  and  will  be  described  together. 

The  urinary  organs  consist  of  a  pair  of  kidneys,  a  pair  of  ureters 
or  Wolffian  ducts  which  join  the  kidneys  with  the  cloaca,  and  a 


72  VERTEBRATE  ZOOLOGY 

urinary  bladder.  The  kidneys  are  narrow  and  greatly  elongated 
bodies  which  lie  in  the  hinder  part  of  the  abdominal  cavity 
close  to  the  dorsal  body  wall.  The  ureter  is  a  convoluted  tube 
which  lies  against  the  outer  edge  of  each  kidney  and  opens  into 
the  dorsal  side  of  the  cloaca.  The  urinary  bladder  is  a  large  sac 
which  opens  into  the  ventral  side  of  the  cloaca  opposite  the 
openings  of  the  ureters.  Note  the  mesentery  which  joins  it 
with  the  ventral  body  wall. 

The  male  genital  organs.  The  testes  are  a  pair  of  yellowish, 
cylindrical  bodies,  each  of  which  is  attached  to  the  dorsal  body 
wall  by  a  mesentery.  Delicate  tubes,  the  vasa  efferentia,  connect 
the  testis  with  the  median  border  of  the  kidney  on  each  side. 
Hold  the  mesentery  to  the  light  and  note  these  vessels,  which 
are  suspended  in  it.  Spermatozoa  are  produced  in  the  testes 
and  pass  through  the  vasa  efferentia  into  the  kidneys,  whence 
they  find  their  way  into  the  WolfBan  ducts  or  ureters.  These 
organs  thus  perform  the  double  function  of  conducting  to  the 
outside  both  the  urine  and  the  spermatozoa;  on  this  account 
they  have  received  a  special  name,  and  are  also  called  ducts  of 
Leydig.  It  is  only  in  elasmobranchs  and  amphibians  that  Ley- 
dig's  duct  is  present. 

The  female  genital  organs.  The  ovaries  are  a  pair  of  irregular, 
elongated  bodies  which  lie  in  the  body  cavity,  attached  to  its 
dorsal  wall  by  mesenteries.  They  vary  in  size  with  the  sexual 
condition  of  the  animal.  The  ova  are  emitted  into  the  body 
cavity  by  the  rupture  of  the  wall  of  the  ovaries,  whence  they 
pass  to  the  outside  through  the  oviducts,  or  Mullerian  ducts.  These 
are  a  pair  of  thick-walled,  convoluted  tubes  which  extend  from 
the  forward  end  of  the  abdominal  cavity  to  the  dorsal  wall  of  the 
cloaca.  The  hinder  end  of  each  is  expanded  and  forms  the  uterus, 
—  a  receptacle  in  which  the  ova  are  stored  at  the  time  of  laying. 

Observe  carefully  these  organs  and  note  their  exact  position. 
Slit  open  the  cloaca  and  find  the  mouths  of  the  ureters,  and  of 
the  oviducts  if  the  animal  be  a  female." 

Exercise  7.  Draw  a  semidiagrammatic  sketch  of  the  urogenital 
system,  showing  accurately  the  position  of  the  urogenital 
organs. 


KECTUBUS  73 

The  respiratory  system.  The  principal  organs  of  respiration 
are  the  outer  skin  and  the  gills.  The  lungs,  which  also  aid  in 
respiration,  are  a  pair  of  very  long  cylindrical  sacs  extending 
back  in  the  abdominal  cavity  from  the  ventral  wall  of  the 
pharynx.  Note  that  the  two  lungs  meet  immediately  before 
they  open  into  the  pharynx  through  the  glottis:  a  windpipe  or 
trachea  is  thus  absent.  Slit  open  one  of  the  lungs  and  note  the 
thinness  of  the  walls.  Examine  carefully  the  structure  and 
mechanism  of  the  glottis. 

Exercise  8.    Draw  the  lungs. 

Remove  the  lungs  and  the  urogenital  organs  from  the  body. 

The  nervous  system.  This  system  is  composed  of  the  follow- 
ing divisions :  (1)  the  central  nervous  system,  consisting  of  the 
brain  and  the  spinal  cord ;  (2)  the  peripheral  nervous  system,  con- 
sisting of  the  cranial  and  spinal  nerves  and  the  sympathetic 
nervous  system;  and  (3)  the  special  sense  organs. 

The  special  sense  organs ;  the  auditory  organs.  The  ear  con- 
sists of  a  membranous  labyrinth  or  inner  ear  alone,  no  external 
opening  being  present.  It  is  relatively  of  large  size  and  may 
be  studied  in  this  dissection.  The  auditory  capsule,  which  in- 
closes the  labyrinth  on  each  side,  is  composed  largely  of  carti- 
lage and  forms  the  hinder  part  of  the  skull. 

The  membranous  labyrinth  is  made  up  of  the  following  parts : 
(a)  the  vestibule,  an  irregular  sac  occupying  the  ventral  and 
middle  portions  of  the  capsule  and  formed  of  two  main  divisions, 
the  upper  utriculus  and  the  lower  sacculus;  (b)  the  semicircular 
canals,  three  delicate  tubes  which  rise  from  the  utriculus  and 
extend  to  the  dorsal  wall  of  the  capsule ;  and  (c)  the  ductus  endo- 
lymphaticus,  a  delicate  tube  which  passes  dorsally  from  the 
sacculus. 

The  auditory  capsules  will  be  recognized  from  the  outside  as 
a  pair  of  prominences  at  the  hinder  end  of  the  skull.  Remove 
the  skin  and  muscles  from  the  dorsal  side  of  the  skull  and  care- 
fully shave  off  the  hard  bone  and  the  cartilage  which  form  the 
roof  of  one  of  the  auditory  capsules.  The  semicircular  canals 
will  first  come  into  view.  Two  of  these  are  medial  in  position 


74  VERTEBRATE   ZOOLOGY 

and  one  lateral.  The  two  medial  canals  are  known  as  the  ante- 
rior and  the  posterior  vertical  canals.  The  anterior  one  is  the 
larger ;  its  forward  end,  close  to  its  junction  with  the  vestibule, 
is  enlarged  and  forms  the  ampulla.  The  posterior  canal  has  an 
ampulla  at  its  hinder  end.  The  lateral  canal  is  called  the  hori- 
zontal canal ;  its  ampulla,  which  is  at  its  forward  end,  is  close  to 
that  of  the  anterior  vertical  canal. 

The  sacculus,  which  forms  the  ventral  portion  of  the  vesti- 
bule, contains  a  large  white  otolith.  At  its  hinder  end  is  a  small 
projection  called  the  lagena,  which  is  homologous  to  the  cochlea 
of  higher  vertebrates. 

Exercise  9.  Draw  the  parts  of  the  ear  so  far  as  observed. 

The  central  nervous  system.  Remove  the  skin  and  muscles 
from  the  dorsal  side  of  the  head  and  the  anterior  end  of  the 
trunk.  Carefully  shave  off  the  bone  and  cartilage  forming  the 
roof  of  the  skull  and  expose  the  brain.  Remove  in  the  same 
way  the  dorsal  portion  of  the  neural  canal  and  expose  the  spinal 
cord.  Remove  the  membrane  (the  dura  mater)  which  covers 
the  brain. 

Without  removing  or  disturbing  it,  study  the  dorsal  surface 
of  the  brain.  It  is  made  up  of  five  regions  of  very  different  size, 
—  the  cerebrum,  thalamencephalon,  the  optic  lobes  or  midbrain, 
the  cerebellum,  and  the  medulla  oblongata. 

The  anterior  and  largest  division  of  the  brain  is  the  cere- 
brum, which  is  composed  of  two  hemispheres ;  no  distinct  olfactory 
lobes  are  present.  Back  of  the  cerebrum  is  a  large  median  struc- 
ture made  up  of  the  thalamencephalon  and  the  midbrain,  no  line  of 
demarcation  between  them  being  present.  Projecting  forward 
from  the  thalamencephalon  between  the  hemispheres  is  the  large 
pineal  body,  or  epiphysis. 

Directly  continuous  with  the  midbrain  posteriorly  and  sepa- 
rated from  it  by  a  shallow  groove  is  the  cerebellum,  a  narrow, 
transverse  ridge  which  forms  the  dorsal  portion  of  the  fourth 
division  of  the  brain.  Immediately  back  of  it  is  the  medulla 
oblongata,  the  hindermost  division,  which  is  continuous  with  the 
spinal  cord.  On  its  dorsal  surface  is  a  triangular  depression,  — 


NECTURUS  75 

the  fossa  rhomboidalis,  —  which  marks  the  position  of  the  fourth 
ventricle  of  the  brain. 

Exercise  10.  Draw  the  dorsal  aspect  of  the  brain  and  a  portion 
of  the  spinal  cord  on  a  scale  of  2  or  3. 

The  cranial  nerves.  Ten  pairs  of  nerves  spring  from  the  brain 
and  pass  to  the  organs  and  tissues  of  the  head  and  the  anterior 
part  of  the  trunk.  Cut  away  the  side  of  the  skull  and  expose 
the  side  of  the  brain ;  find  the  cranial  nerves. 

The  first  pair  of  cranial  nerves  are  the  olfactories;  they  are 
large  nerves  which  pass  directly  forward  from  the  anterior  end 
of  the  hemispheres  to  the  nasal  capsules,  in  some  cases  branch- 
ing before  they  reach  the  capsules.  The  second  pair  are  the 
optic  nerves;  these  nerves  are  small,  and  will  be  seen  emer- 
ging from  the  brain  just  back  of  the  cerebrum  and  passing  to 
the  orbits.  The  third  nerve  —  the  oculomotor  —  is  a  very  small, 
threadlike  nerve  which  arises  on  the  ventral  surface  of  the 
brain  beneath  the  midbrain  on  each  side,  and  passes  forward  to 
the  orbit,  where  it  supplies  the  muscles  of  the  eyeball.  The 
fourth  cranial  nerve,  the  trochlear,  and  the  sixth,  the  abducens, 
are  wanting  in  Necturus,  both  being  incorporated  in  the  fifth 
nerve. 

The  fifth  cranial  nerve  —  the  trigeminus  —  is  a  large  trunk 
which  passes  forward  a  short  distance  and  then  expands  in  the 
Gasserian  ganglion,  which  lies  against  the  inner  wall  of  the  skull. 
It  then  splits  into  two  main  branches,  —  an  ophthalmic  and  a 
maxillo-mandibular  branch,  which  pass  to  the  outside  of  the  skull ; 
trace  them  as  far  as  possible. 

The  seventh  or  facial  and  the  eighth  or  auditory  nerves  spring 
from  the  brain  as  a  single  trunk,  which,  after  sending  off 
a  large  branch  to  the  Gasserian  ganglion,  divides  into  two 
nerves,  —  the  facial  and  the  auditory.  The  former  soon  splits 
into  two  branches ;  the  latter  at  once  enters  the  auditory 
capsule. 

The  ninth  and  tenth  nerves  —  the  glossopharyngeal  and  the 
vagus  —  spring  from  the  brain  immediately  back  of  the  facial 
and  auditory  trunk  by  three  roots  and  at  once  unite  to  form 


76  VERTEBRATE  ZOOLOGY 

a  single  large  nerve.  This  passes  back  a  short  distance  and 
then  expands  to  form  a  large  ganglion,  from  which  numerous 
nerves  pass  to  the  tongue,  neck,  and  gills,  and  to  the  heart  and 
stomach. 

Observe  the  anterior  spinal  nerves.  Each  one  arises  from 
the  side  of  the  spinal  cord  by  two  roots,  —  a  dorsal  and  a 
ventral  root,  in  the  former  of  which  is  a  ganglion.  These 
roots  pass  out  of  the  neural  canal  by  the  foramina  between 
the  vertebrae. 

Exercise  11.  Draw  the  cranial  nerves  and  the  first  two  or  three 
spinal  nerves  so  far  as  they  have  been  observed. 

The  ventral  surface  of  the  brain.  Carefully  remove  the  brain 
from  the  skull,  float  it  in  water,  and  study  its  ventral  surface. 
The  large  paired  hemispheres  will  be  seen  and  back  of  them  the 
median  thalamencephalon,  from  which  the  small  optic  nerves  and 
the  infundibulum  proceed.  The  latter  is  a  large  median  projec- 
tion just  back  of  the  optic  nerves  which  bears  at  its  distal  end 
a  small  body  called  the  pituitary  body,  or  hypophysis.  This  struc- 
ture rests  in  a  depression  in  the  ventral  wall  of  the  skull  and 
is  apt  to  be  torn  away  when  the  skull  is  removed.  Back 
of  the  infundibulum  are  the  crura  cerebri,  two  swellings  which 
join  the  medulla;  they  form  the  ventral  portion  of  the  mid- 
brain.  Note  the  midventral  groove  in  the  medulla  and  the 
spinal  cord. 

Exercise  12.  Draw  the  ventral  aspect  of  the  brain  on  a  scale  of 
2  or  3. 

The  cavities  of  the  brain  and  spinal  cord.  The  brain  and  spinal 
cord  are  hollow  structures.  In  the  center  of  the  latter  is  a  nar- 
row passage  called  the  central  canal,  while  the  brain  contains  a 
series  of  large  spaces  of  various  sizes.  In  the  medulla  is  the 
broad,  shallow  cavity  called  the  fourth  ventricle.  Its  dorsal  roof 
is  not  composed  of  nervous  matter  but  is  vascular,  and  hence 
dark  colored.  The  cavities  of  the  hemispheres  are  called  the 
lateral  or  the  first  and  second  ventricles.  These  are  joined  with 


NECTURUS  77 

each  other  and  also  with  the  small  median  cavity  of  the  thala- 
mencephalon,  which  is  called  the  third  ventricle,  by  a  small  open- 
ing called  the  foramen  of  Monro.  Joining  the  third  ventricle  with 
the  fourth  is  a  median  canal  called  the  aqueductus  Sylvii,  with 
which  are  connected  a  pair  of  large  cavities  situated  in  the 
optic  lobes  or  midbrain  and  called  the  optic  ventricles. 

The  fourth  ventricle  has  already  been  seen.  The  lateral  ven- 
tricles are  found  by  removing  the  dorsal  wall  of  the  hemispheres, 
and  the  optic  ventricles  by  removing  the  dorsal  wall  of  the 
optic  lobes.  The  median  spaces  are  not  so  easy  to  find,  but  may 
be  seen  by  splitting  the  brain  exactly  in  the  sagittal  plane. 

Exercise  13.  Draw  a  diagram  showing  the  cavities  of  the  brain. 

The  vascular  system  is  made  up  of  the  following  organs: 
(1)  the  heart ;  (2)  the  arteries,  which  carry  blood  to  the  gills, 
the  lungs,  and  the  tissues ;  (3)  the  veins,  which  return  blood  to 
the  heart;  and  (4)  the  capillaries. 

The  heart.  The  divisions  of  the  heart  have  already  been  ob- 
served and  its  ventral  aspect  studied  (see  page  69). 

The  veins.  Two  systems  of  veins  are  present :  (1)  the  systemic 
veins,  which  return  venous  blood  from  the  various  tissues  and 
organs  of  the  body  to  the  sinus  venosus ;  and  (2)  the  pulmonary 
veins,  which  return  arterial  blood  from  the  lungs  to  the  left 
auricle.  The  systemic  veins  include  (a)  those  which  go  directly 
to  the  sinus  venosus  and  their  branches,  and  (b)  the  portal  veins, 
which  carry  blood  first  to  the  liver  and  kidneys,  where  it  is  dis- 
tributed through  capillaries  and  afterward  collected  again  in 
other  veins  which  take  it  to  the  heart. 

We  shall  first  study  the  portal  veins.  Two  systems  of  these 
veins  are  present,  —  the  hepatic  portal  system,  by  which  blood  is 
carried  from  the  digestive  organs  and  the  spleen  to  the  liver; 
and  the  renal  portal  system,  by  which  it  is  carried  from  the  hind 
quarters  of  the  body  to  the  kidneys.  These  two  systems  are 
united  by  the  abdominal  vein,  a  prominent  vessel  which  lies  in  the 
midventral  line  of  the  abdominal  cavity  back  of  the  liver. 

Kill  a  fresh  animal  and  skin  its  ventral  side.  Note  the  ab- 
dominal vein,  which  may  usually  be  seen  through  the  body 


78  VEBTEBRATE  ZOOLOGY 

wall  of  the  hinder  part  of  the  abdominal  cavity.  Open  this 
cavity  by  a  longitudinal  incision  to  one  side  of  the  abdom- 
inal vein.1 

Cut  the  mesentery  which  joins  the  liver  with  the  ventral 
body  wall,  —  being  careful  not  to  cut  the  abdominal  vein,  which 
lies  in  it,  —  press  the  sides  of  the  body  wall  to  the  right  and 
left  and  pin  them  there. 

The  hepatic  portal  system  is  composed  of  the  hepatic  portal  vein 
and  its  branches  and  the  abdominal  vein,  —  the  former  bringing 
blood  from  the  digestive  tract  and  the  spleen  and  the  latter 
from  the  hinder  part  of  the  body.  These  two  y,eins  meet  near 
the  posterior  end  of  the  duodenum,  close  to  the  dorsal  surface 
of  the  liver;  they  are  here  entirely  imbedded  in  the  pancreas. 
The  single  vessel  thus  formed  passes  at  once  to  the  liver,  where 
it  breaks  up  into  branches  which  distribute  blood  to  all  parts  of 
that  organ. 

Follow  the  abdominal  vein  forward  to  the  hepatic  portal. 
Scrape  away  the  pancreas  which  surrounds  them,  and  note  that 
the  hepatic  portal  is  formed  by  the  meeting  of  three  large  veins, 
—  the  mesenteric,  gastric,  and  splenic. 

The  mesenteric  vein  is  the  large  longitudinal  vein  which  lies  in 
the  intestinal  mesentery;  it  extends  the  entire  length  of  the 
intestine  and  receives  numerous  intestinal  veins  which  bring  blood 
from  its  walls.  The  splenic  vein  comes  from  the  spleen.  The 
gastric  vein  lies  along  the  stomach  and  the  dorsal  surface  of  the 
liver. 

The  renal  portal  system  is  formed  on  each  side  of  the  body  by 
the  union  of  the  pelvic,  femoral,  and  caudal  veins,  which  meet  and 
form  the  renal  portal  vein ;  the  system  is  joined  with  the  hepatic 
portal  system  by  the  abdominal  vein. 

1  Both  portal  systems  may  be  injected  through  either  the  abdominal  vein  or 
the  mesenteric  vein.  If  the  former  be  used,  it  must  be  injected  both  forward 
and  backward ;  if  the  latter,  a  single  injection  will  fill  both  portal  systems. 
The  systemic  veins  and  the  arteries  should  also  be  injected  now.  Turn  the  liver 
to  the  animal's  left ;  the  very  large  postcaval  vein  will  be  seen  coming  from 
between  the  kidneys  and  entering  the  liver  near  its  middle.  Inject  it  in  both 
directions.  The  entire  arterial  system  may  be  injected  through  the  ventricle 
and  the  truncus  arteriosus  of  the  heart. 


NECTURUS  79 

Trace  this  last-named  vein  back  to  the  hinder  part  of  the 
abdominal  cavity;  it  will  be  seen  to  be  formed  by  the  union 
of  two  prominent  veins,  —  the  right  and  left  pelvic  veins,  —  one 
of  which  will  have  been  cut  by  the  first  incision.  Trace  the 
pelvic  vein  backward ;  it  is  formed  by  the  union  of  the  femoral 
vein,  which  comes  from  the  hind  leg,  and  the  renal  portal  vein, 
which  goes  to  the  side  of  the  kidney.  This  vein  enters  the 
kidney  and  distributes  blood  throughout  that  organ. 

Blood  from  the  tail  is  brought  forward  by  the  caudal  vein. 
This  vein  runs  just  beneath  the  spinal  column  of  the  tail  to  the 
hinder  end  Qf  the  abdominal  cavity;  here  it  divides  into  two 
veins,  each  of  which  goes  to  the  side  of  the  kidney  and  joins  the 
renal  portal  vein. 

Exercise  14.  Draw  the  two  portal  systems. 

The  remaining  systemic  veins  may  be  divided  into  two  groups, 
—  those  coming  to  the  heart  from  the  forward  part  of  the  body 
and  those  coming  from  the  hinder  part. 

The  latter  veins  are  the  postcaval,  the  posterior  cardinal,  and 
the  lateral  veins.  The  postcaval  is  the  largest  vein  in  the  body ; 
it  begins  its  course  between  the  kidneys,  from  which  it  receives 
numerous  small  branches,  and  runs  forward,  just  beneath  the 
dorsal  aorta,  to  the  middle  of  the  dorsal  surface  of  the  liver. 
Here  it  turns  slightly  to  the  right,  enters  the  liver  and  runs 
through  it  to  its  forward  end,  receiving  several  hepatic  veins. 
On  leaving  the  liver  it  becomes  much  wider  and  divides  into 
two  short  trunks,  which  at  once  enter  the  sinus  venosus.  Find 
this  vein  just  back  of  the  liver  and  trace  it  both  ways. 

Between  the  kidneys  and  the  liver  the  postcaval  receives  a 
number  of  small  genital  veins  from  the  reproductive  organs  and 
a  branch  from  each  of  the  posterior  cardinal  veins. 

The  posterior  cardinals  are  a  pair  of  veins  which  arise  near  the 
middle  of  the  body  and  run  forward  at  the  right  and  the  left 
of  the  median  plane  and  near  the  dorsal  body  wall ;  in  the  female 
each  posterior  cardinal  lies  in  the  mesentery  which  joins  the 
oviduct  with  the  dorsal  body  wall  on  each  side.  A  short  dis- 
tance in  front  of  the  anterior  end  of  the  liver  each  of  these 


80  VERTEBRATE  ZOOLOGY 

veins  joins  a  short  transverse  vein  called  the  duct  of  Cuvier,  which 
meets  the  widened  end  of  the  postcaval  near  its  entrance  into 
the  sinus  venosus. 

The  lateral  veins  are  a  pair  of  small  vessels,  each  of  which 
lies  beneath  the  skin  along  the  lateral  line ;  they  enter  the  duct 
of  Cuvier. 

Blood  is  brought  from  the  forward  part  of  the  body  by  the 
anterior  cardinal  and  the  subclavian  veins.  The  former  are  a  pair 
of  short  veins  which  arise,  on  each  side,  by  the  union  of  the 
internal  and  the  external  jugular  veins.  The  external  jugular  is 
the  large  vein  which  brings  blood  from  the  ventral  wall  of 
the  mouth ;  the  internal  jugular  is  a  much  smaller  vein  which 
brings  blood  from  the  roof  of  the  mouth  and  the  brain.  The 
subclavian  brings  blood  from  the  arm  on  each  side ;  it  and  the 
anterior  cardinal  meet  in  the  duct  of  Cuvier. 

The  pulmonary  vein  brings  blood  to  the  left  auricle  from  the 
lungs.  It  is  formed  by  the  union  of  the  right  and  left  pul- 
monary veins,  which>come  from  the  right  and  left  lungs  respec- 
tively. Each  of  these  veins  is  a  prominent  vessel  which  lies  on 
the  inner  side  of  the  lung.  Find  it  here  and  trace  it  forward. 

Exercise  15.  Draw  a  diagram  of  these  veins  so  far  as  observed. 

The  arteries.  Two  systems  of  arteries  are  present :  by  one  of 
these  systems  blood  is  carried  from  the  heart  to  the  gills  and 
by  the  other  from  the  gills  to  the  tissues.  The  pulmonary 
arteries  belong  to  the  last-named  system. 

Running  forward  as  a  continuation  of  the  truncus  arteriosus 
is  the  ventral  aorta,  a  large  artery  which  lies  in  the  median  plane 
between  the  gills.  At  its  forward  end  this  vessel  breaks  into 
two  pairs  of  branches.  The  foremost  pair  are  the  first  pair  of 
afferent  branchial  arteries,  which  carry  blood  to  the  first  pair  of 
gills.  The  hinder  and  larger  pair  soon  divides  and  gives  rise  to 
two  pairs  of  arteries,  the  second  and  'third  pairs  of  afferent 
branchial  arteries  which  go  to  the  second  and  third  pairs  of  gills. 
Find  these  arteries  and  study  their  relation  to  the  gill  arches. 

The  blood,  after  having  passed  through  the  gills,  is  collected 
in  three  pairs  of  efferent  arteries,  which  carry  it  away  from  the 


NECTURUS  81 

gills.  Find  them  and  note  their  relation  to  the  gill  arches  and 
to  the  afferent  arteries.  The  foremost  efferent  artery  on  each 
side  gives  off  two  arteries  which  pass  straight  forward  to  the 
head,  —  the  smaller  being  the  internal  carotid  and  the  larger  the 
external  carotid.  The  second  and  third  efferent  arteries  unite 
and  form  a  single  vessel,  which  is  joined  with  the  first  efferent 
artery  by  means  of  a  short  connecting  artery.  A  short  distance 
beyond  the  point  of  junction  the  single  vessel  thus  formed  gives 
off  the  large  pulmonary  artery;  it  then  becomes  the  aortal  arch 
and,  meeting  its  fellow  of  the  opposite  side,  forms  the  dorsal 
aorta.  The  pulmonary  artery  passes  straight  back  along  the 
dorsal  side  of  the  lung. 

The  dorsal  aorta  runs  back  just  beneath  the  spinal  column  to 
the  hinder  end  of  the  animal ;  in  the  tail  it  becomes  the  caudal 
artery.  At  regular  intervals,  corresponding  to  the  vertebrae,  a 
pair  of  small  spinal  arteries  springs  from  the  dorsal  side  of  the 
aorta  and  supplies  the  body  muscles.  ^ 

A  short  distance  back  of  its  point  of  origin  the  aorta  sends  off 
a  pair  of  subclavian  arteries,  which  go  to  the  fore  legs.  Each  sub- 
clavian  also  gives  off  near  its  base  the  cutaneous  artery,  which 
passes  back  in  the  body  wall  near  the  midventral  plane  and 
supplies  the  skin  with  blood;  the  outer  ends  of  the  spinal 
arteries  anastomose  with  it. 

The  next  large  artery  to  leave  the  aorta  is  the  gastric  artery, 
which  supplies  the  stomach.  Near  the  center  of  the  abdominal 
cavity  the  large  coeliaco-mesenteric  artery  leaves  the  aorta  and  goes 
to  the  stomach,  spleen,  and  intestine.  The  intestine  is  also 
supplied  with  blood  by  the  posterior  mesenteric  arteries,  which  are 
about  twenty  in  number  and  branch  off  from  the  hinder  portion 
of  the  aorta.  In  most  of  the  higher  vertebrates  a  single  posterior 
mesenteric  trunk  is  present.  The  numerous  genital  arteries  and 
renal  arteries  also  branch  off  from  the  hinder  portion  of  the  aorta 
and  supply  the  genital  organs  and  the  kidneys.  The  large  iliac 
arteries  leave  the  hinder  end  of  the  aorta  and  go  to  the  hind  legs. 

Exercise  16.  Draw   a  semidiagrammatic   sketch  of   the   entire 
arterial  system. 


82  VEBTEBEATE  ZOOLOGY 

The  muscular  system.  Remove  the  skin  from  the  entire  body 
of  a  Necturus.  Inasmuch  as  the  skin  adheres  very  tightly  to 
muscles  beneath,  care  must  be  taken  not  to  cut  the  latter,  espe- 
cially on  the  lower  jaw  and  the  breast.  Begin  with  a  median 
incision  down  the  back  of  the  animal  and  skin  toward  the  ven- 
tral side. 

Observe  the  great  complex  muscle  which  forms  the  side  of 
the  trunk  and  the  tail.  It  will  be  seen  to  be  made  up  of  a 
succession  of  muscle  segments  which  are  called  myotomes  or 
myomeres  arid  are  separated  from  one  another  by  connective-tissue 
septa  called  myocommas.  Each  myotome  is  a  plate  between  two 
myocommas,  and  consists  of  parallel  muscle  fibers  which  run 
across  from  one  myocomma  to  the  other.  The  body  muscula- 
ture of  the  trunk  and  the  tail  is  essentially  like  that  of  the  fish. 
In  the  midventral  line  is  a  white  line  —  the  linea  alba  —  which 
divides  the  muscles  on  the  right  side  from  those  on  the  left. 

In  the  region  of  the  head,  the  legs,  and  the  arms,  specialized 
muscles  are  present.  The  entire  ventral  surface  of  the  lower 
jaw  is  bounded  by  a  broad,  thin  muscle,  the  submandibular,  the 
fibers  of  which  have  a  transverse  direction  and  are  divided  by  a 
median  tendon  into  two  parts.  Split  this  muscle  in  the  median 
line  and  remove  the  left  half  so  that  the  muscles  beneath  will 
be  exposed.  Two  muscles  will  be  seen,  —  the  geniohyoid  and  the 
ceratohyoid.  The  former  is  a  narrow  muscle  with  longitudinal 
fibers  which  extends  from  the  tip  of  the  lower  jaw  to  the  hyoid 
cartilage ;  the  latter  is  a  thick  muscle  with  an  oblique  direction 
which  passes  from  the  hyoid  cartilage  to  the  first  gill  arch. 

In  the  region  of  the  fore  limbs  will  be  seen  the  pectorals,  a  pair 
of  fan-shaped  muscles  whose  fibers  radiate  from  the  forward 
side  of  the  arm  to  the  midventral  line ;  they  draw  the  arms 
backward.  The  opposing  muscles,  which  draw  the  arms  forward, 
are  the  slender  procoraco-humeralis  muscles.  These  will  be  seen  ex- 
tending directly  forward  from  the  base  of  the  arm  to  the  pro- 
coracoid  cartilages. 

Note  in  this  region  the  coracoid  and  the  procoracoid  cartilages, 
which  are  portions  of  the  pectoral  girdle  ;  they  are  very  thin 
plates  which  underlie  the  muscles  just  mentioned. 


NECTUKUS  83 

On  the  upper  arm  note  the  two  muscles  which  appear  on  its 
ventral  surface.  The  anterior  muscle  is  the  flexor,  and  the  pos- 
terior one  is  the  extensor  of  the  forearm  and  hand.  On  the 
forearm  note  that  but  a  single  muscle  is  present  on  the  ven- 
tral side ;  this  is  the  flexor  of  the  hand.  In  the  higher  verte- 
brates this  muscle  is  divided  into  a  number  which  flex  the  fingers 
separately. 

In  the  region  of  the  hind  legs  are  the  femoral  muscles,  a  pair 
of  fan-shaped  muscles  which  extend  from  the  base  of  the  legs 
to  the  median  line.  Extending  from  the  posterior  border  of  these 
muscles  to  the  anus  are  the  pyriform  muscles. 

Exercise  17.   Draw  the  ventral  aspect  of  the  animal,  showing 
these  muscles. 

The  skeletal  system.  This  system  is  composed  of  two  dis- 
tinct portions,  the  exoskeleton  and  the  endoskeleton.  The  former 
is  but  very  slightly  developed  in  Necturus,  as  in  most  amphib- 
ians. Bony  or  horny  scales  or  other  hardened  integumentary 
structures,  which  form  the  exoskeleton  in  all  other  classes  of 
vertebrates,  are  not  present,  the  outer*  surf  ace  of  the  body  being 
protected  only  by  the  secretions  of  the  slime  glands.  Claws 
are  also  absent.  The  only  exoskeletal  structures  present  are  the 
teeth  and  certain  bones  of  the  skull  called  membrane  bones; 
these  are,  however,  so  closely  joined  with  the  other  bones  of  the 
skull  that  they  will  be  considered  with  them. 

The  endoskeleton  consists  of  the  bones  and  cartilages  which 
form  the  framework  of  the  body.  It  may  be  divided  into  (1)  the 
axial  skeleton,  which  includes  the  skull  and  the  vertebral  column 
and  the  ribs,  and  (2)  the  appendicular  skeleton,  which  includes  the 
framework  of  the  two  pairs  of  appendages  or  limbs. 

We  shall  first  study  the  appendicular  skeleton.  Each  pair 
of  appendages  is  composed  of  the  two  limbs  and  the  girdle  by 
which  they  are  joined  with  the  trunk,  the  girdle  of  the  anterior 
appendages  being  the  pectoral  or  shoulder  girdle,  that  of  the  pos- 
terior appendages  being  the  pelvic  girdle. 

The  anterior  extremities.  The  pectoral  girdle  consists  of  a 
pair  of  delicate  triradiate  structures,  composed  principally  of 


84  VEKTEBEATE  ZOOLOGY 

cartilage,  which  lie  on  the  ventral  and  lateral  sides  of  the  trunk. 
Each  half  of  the  girdle  supports  an  arm  and  consists  of  a  single 
skeletal  piece  which  is  imbedded  in  the  muscles  of  the  trunk 
and  is  not  joined  with  the  other  half  or  with  the  axial  skeleton ; 
at  about  the  middle  of  it  is  a  depression,  the  glenoid  fossa,  which 
receives  the  head  of  the  humerus  and  forms  the  shoulder  joint. 

Each  half  of  the  pectoral  girdle  is  made  up  of  a  dorsal  por- 
tion —  the  scapula  —  and  two  ventral  portions  —  the  coracoid  and 
the  procoracoid.  The  scapula  is  composed  of  two  distinct  parts, 
—  a  narrow  ventral  portion,  which  is  of  bone,  and  a  broad  dorsal 
cartilaginous  portion.  The  procoracoid  is  a  narrow  strip  of  car- 
tilage extending  directly  forward ;  the  coracoid  is  a  broad  plate 
of  cartilage  posterior  to  the  procoracoid  and  extending  medially. 
The  coracoids  of  the  two  sides  overlap  each  other,  the  left  one 
being  usually  ventral  to  the  right  one.  The  coracoid  lies  beneath 
the  pectoral  muscle  and  the  procoracoid  beneath  the  procoraco- 
humeralis  muscle. 

A  sternum  is  present  but  is  very  slightly  developed.  It  con- 
sists of  two  or  more  irregular,  very  delicate  cartilages,  which 
appear  in  the  myocommas  beneath  the  medial  ends  of  the  cor- 
acoids in  the  ventral  body  wall. 

Observe  the  muscles  on  the  dorsal  side  of  the  arm  and  shoul- 
der, on  the  right  side  of  the  body.  Determine  accurately  the 
outlines  of  the  coracoid  and  the  procoracoid  beneath  the  muscles. 
The  outlines  of  the  scapula  will  also  be  easily  determined  by 
moving  the  arm  back  and  forth.  Pass  a  scalpel  beneath  the 
different  parts  of  the  girdle  on  this  side  and  remove  both  girdle 
and  leg  from  the  trunk,  taking  care  not  to  injure  them. 

Carefully  remove  the  muscles  from  the  girdle  and  identify 
the  three  parts  and  the  glenoid  cavity  in  which  the  humerus 
articulates.  Note  the  foramen  coracoideum,  —  a  small  hole  through 
which  a  nerve  passes. 

Exercise  18.  Draw  the  pectoral  girdle. 

Remove  the  muscles  from  the  arm,  but  do  not  separate  its 
bones  from  one  another.  The  skeleton  of  the  arm  is  made 


NECTURUS  85 

up  of  three  divisions,  —  a  proximal,  a  middle,  and  a  distal.  The 
proximal  division,  or  the  upper  arm,  is  a  single  bone,  the  humerus, 
the  articular  ends  of  which  are  cartilaginous ;  its  proximal  end 
or  head  articulates  with  th^  glenoid  cavity.  Note  the  difference 
in  the  form  of  the  articular  surfaces  of  the  two  ends.  The  middle 
division,  or  forearm,  is  composed  of  two  bones,  —  the  radius  and 
ulna,  —  the  ends  of  which  are  cartilaginous.  Of  these,  the  radius 
is  anterior  or  pre axial  in  position ;  the  ulna  is  postaxial  and  is 
prolonged  at  its  proximal  end  to  form  the  olecranon  process,  which 
forms  the  elbow. 

The  distal  division  includes  the  wrist  and  hand.  The  wrist, 
or  carpus,  is  composed  of  six  small  cartilages,  two  of  which  form 
a  transverse  proximal  row,  three  a  distal  row,  while  one  is  in 
the  center.  In  the  typical  vertebrate  carpus  three  bones  form 
the  proximal  row,  five  the  distal  row,  and  one  or  two  are  in  the 
center.  In  the  hand  of  Necturus  four  digits  are  present,  each 
of  which  is  composed  of  a  proximal  bone  called  the  metacarpal 
and  two  or  three  distal  bones  which  are  called  the  phalanges,  or 
finger  bones.  In  the  typical  vertebrate  hand  five  digits  are  pres- 
ent, —  the  digit  which  is  lacking  in  the  hand  of  Necturus  being 
the  first  or  thumb. 

Exercise  19.  Draw  the  arm  on  a  scale  of  2  or  3,  showing  accu- 
rately the  outline  of<»each  bone  and  cartilage. 

The  posterior  extremities.  The  pelvic  girdle  is  different  in  shape 
from  the  pectoral  girdle.  It  consists  of  a  large  ventral  plate,  — 
the  pubo-ischium,  —  which  lies  between  the  hind  legs  in  the  ven- 
tral body  wall,  and  a  slender  rod  on  each  side  called  the  ilium, 
which  extends  from  the  ventral  plate  upward  to  the  spinal 
column.  The  pelvic  girdle,  like  the  pectoral,  is  a  paired  struc- 
ture, and  is  composed  of  three  skeletal  pieces  on  each  side,  —  a 
dorsal  piece  and  two  ventral  ones.  The  dorsal  piece  is  the  ilium  : 
it  is  a  slender  rod  of  bone  and  cartilage ;  the  ventral  pieces 
are  the  pubis  and  ischium,  which  form  the  pubo-ischium,  —  the 
forward  portion  of  that  structure  being  the  two  pubes  and  the 
hinder  portion  the  two  ischia.  Near  the  base  of  the  ilium,  on 


86  VERTEBRATE   ZOOLOGY 

each  side,  is  the  acetatmlum, —  the  articular  surface  of  the  femur ; 
a  short  distance  in  front  of  this  is  a  small  hole,  the  obturator 
foramen.  The  greater  part  of  the  pubo-ischium  is  composed  of 
cartilage ;  a  pair  of  bones  is,  however,  present  in  the  hinder  or 
ischial  portion. 

The  two  ilia  articulate  with  a  single  vertebra  by  means  of  its 
ribs.  This  vertebra,  which  is  called  the  sacrum,  is  usually  the 
nineteenth.  In  some  cases  the  two  ilia  do  not  go  to  the  same 
vertebra  but  to  two  successive  ones. 

Remove  the  thin  layer  of  muscles  which  covers  the  ventral 
portion  of  the  pelvis,  and  expose  it.  Be  careful  not  to  injure  its 
anterior  end,  which  runs  to  a  point.  Remove  all  the  muscles 
in  this  region  and  expose  the  spinal  column  and  the  ilium. 
Find  the  articulation  of  the  ilia  with  the  sacrum  ;  disarticu- 
late the  ilia  and  remove  the  pelvic  girdle  with  the  legs  from 
the  body. 

Exercise  20.  Draw  the  pelvic  girdle  and  carefully  label  its  vari- 
ous parts. 

Remove  the  muscles  from  the  leg,  but  do  not  separate  the 
bones  of  the  leg  from  one  another.  The  skeleton  of  the  leg  is 
composed  of  three  divisions,  —  a  proximal,  a  middle,  and  a  distal. 
The  proximal  division,  or  thigh,  is  a  single  bone,  —  the  femur,  — 
the  ends  of  which  are  of  cartilage ;  its  proximal  end  articulates 
with  the  acetabulum  and  forms  the  hip  joint.  In  the  middle 
division,  or  shank,  are  two  bones,  —  the  tibia  and  the  fibula,  — 
the  ends  of  which  are  cartilaginous,  the  tibia  being  anterior  or 
preaxial  in  position. 

The  distal  portion  is  composed  of  the  ankle  and  the  foot. 
The  ankle  is  made  up  of  six  small  cartilages  called  the  tarsals, 
two  of  which  form  a  transverse,  proximal  row,  three  a  distal 
row,  while  one  is  in  the  center.  The  typical  number  of  bones 
or  cartilages  in  the  vertebrate  tarsus  is  ten,  three  being  in  the 
proximal  and  five  in  the  distal  row,  while  one  or  two  are  in 
the  center.  In  the  foot  of  Necturus  four  digits  are  present, 
each  of  which  is  composed  of  a  proximal  metatarsal  bone  and 


KECTUEUS  87 

two  or  three  phalanges  or  toe  joints.  In  the  typical  vertebrate 
foot  five  digits  are  present.  The  digit  which  is  lacking  in  the 
foot  of  Necturus  is  the  first. 

Exercise  21.  Draw  an  outline  of  the  skeleton  of  the  leg  on  a 
scale  of  2  or  3,  showing  accurately  the  bones  and  cartilages. 

The  axial  skeleton.    The  skull  is  made  up  of  two  regions,  — 
the  cranium  and  the  visceral  skeleton.    The  former  incloses  and 
protects  the  brain  and  the  organs  of  special  sense ;  the  latter 
surrounds  the  mouth  and  pharynx,  forming  the  framework  of 
the  jaws  and  the  hyobranchial  apparatus. 

Both  of  these  regions  are  composed  entirely  of  cartilage  in 
an  early  period  of  the  animal's  life,  and  certain  portions  remain 
cartilaginous,  —  this  primitive  cartilaginous  skull  being  called 
the  chondrocranium.  As  the  young  animal  develops,  however, 
certain  parts  of  the  cartilage  are  replaced  by  bone.  Besides 
these  cartilage  bones,  as  they  are  called,  other  bones  also  make 
their  appearance  which  develop,  not  in  the  cartilage,  but  in  the 
skin  and  in  connective-tissue  membranes  which  cover  the  skull : 
these  are  called  membrane  bones.  Thus,  so  far  as  the  material  of 
which  it  is  made  up  is  concerned,  the  skull  is  composed  of  carti- 
lage, cartilage  bones,  and  membrane  bones. 

Open  the  body  cavity  and  remove  the  viscera.  Strip  off  all 
the  muscles  from  the  skeleton.  It  is  well  to  begin  the  process 
with  the  head,  and  to  lay  bare  and  study  first  the  hyoid  and  gill 
arches  which  together  form  the  hyobranchial  apparatus,  and 
then  the  lower  jaw.  These  parts  constitute  the  ventral  portion  of 
the  skull  and  belong  to  the  visceral  skeleton.  The  skull  must 
be  kept  in  preserving  fluid  and  not  be  allowed  to  get  dry. 

The  lower  jaw,  or  mandible,  is  a  paired  arch-shaped  structure 
composed  on  each  side  of  three  bones  and  a  cartilage.  The  bones 
are  the  following  :  the  dentary,  —  a  large  bone  which  forms  the 
anterior  and  nearly  all  of  the  outer  surface  of  the  mandible  and 
bears  most  of  the  teeth;  the  splenial,  —  a  small  plate  of  bone 
on  the  inner  surface  of  the  mandible  near  its  middle,  which 
bears  the  hindermost  teeth ;  and  the  angular,  which  is  on  the 


88  VERTEBRATE   ZOOLOGY 

inner  surface  of  the  mandible,  extending  from  its  hinder  end 
forward  about  two  thirds  of  its  length.  These  bones  are  all 
membrane  bones ;  they  overlay  the  cartilage.  This  is  Meckel's 
cartilage ;  it  forms  the  axis  of  the  mandible  and  is  exposed  to 
view 'on  its  inner  side  and  at  its  hinder  end,  where  it  articulates 
with  the  upper  part  of  the  skull. 

The  hyobranchial  apparatus  is  an  extensive  cartilaginous  and 
bony  structure  which  lies  back  of  the  mandible  in  the  ventral 
body  wall  and  supports  the  tongue  and  the  gills.  The  whole 
structure  is  composed  of  four  arches,  all  cartilaginous,  the  two 
foremost  of  which  are  complete,  the  right  and  left  halves  meet- 
ing in  the  median  line,  and  lying  parallel  with  the  arch-shaped 
mandible,  while  the  hindermost  two  are  incomplete  and  lie 
parallel  with  the  outer  ends  of  the  foremost  arches.  A  slender 
median  cartilage  joins  the  two  foremost  arches,  and  a  median 
rod  of  bone  extends  back  from  the  second  one. 

The  foremost  of  these  arches  is  the  hyoid  arch:  it  supports 
the  tongue.  It  consists  of  a  right  and  a  left  half,  each  of  which 
is  made  up  of  two  bars  of  cartilage,  —  a  short  medial  bar,  the 
hypohyal  cartilage,  and  a  long  lateral  one,  the  ceratohyal. 

The  second  arch  is  the  first  branchial  or  gill  arch ;  each  half  is 
composed  also  of  two  bars  of  cartilage,  —  a  long  medial  bar,  the 
ceratobranchial  cartilage,  and  the  long  lateral  epibranchial.  The  third 
arch  is  the  second  branchial  arch.  It  is  incomplete,  the  two  halves 
not  meeting  in  the  median  line ;  each  half  is  made  up  of  a 
minute  ceratobranchial  and  a  long  epibranchial,  both  of  which  lie 
back  of  and  parallel  with  the  first  epibranchial  cartilage.  The 
fourth  and  last  arch  is  the  third  branchial  arch ;  it  is  also  incom- 
plete, consisting  of  a  single  epibranchial  cartilage  on  each  side 
which  lies  just  back  of  the  second  epibranchial. 

The  two  median  pieces  are  the  first  and  second  basibranchials, 
the  first  being  the  median  cartilaginous  bar  which  joins  the 
hyoid  with  the  first  branchial  arch,  and  the  second  a  slender 
median  bone  just  posterior  to  the  first  branchial  arch. 

Exercise  22.  Draw  the  mandible  and  the  hyobranchial  apparatus 
on  a  scale  of  2. 


NECTUEUS  89 

Thoroughly  clean  the  remainder  of  the  skull  and  the  anterior 
portion  of  the  spinal  column.  Disarticulate  the  head  from  the 
spinal  column. 

Observe  the  flatness  of  the  skull  and  its  compactness.  The 
cranial  bones  and  cartilages  are  intimately  joined  with  the  remain- 
ing bones  of  the  visceral  skeleton,  the  whole  forming  so  closely 
knit  a  structure  that  its  various  parts  are  not  easy  to  separate 
from  one  another.  At  the  hinder  end  is  the  foramen  magnum,  the 
large  opening  through  which  the  spinal  cord  enters  the  brain 
cavity;  at  the  forward  end  are  two  rows  of  small  teeth.  The 
cranial  portion  of  the  skull,  which  incloses  and  protects  the 
brain  and  the  special  sense  organs,  forms  the  medial  and  larger 
part  of  it.  The  upper  jaw  and  other  portions  of  the  visceral 
skeleton  occupy  the  two  lateral  areas. 

This  part  of  the  skull,  like  the  lower  jaw  and  the  hyobranchial 
apparatus  which  have  been  already  studied,  is  composed  very 
largely  of  cartilage.  Of  the  bones  present  the  greater  number 
are  membrane  bones,  these  being  mostly  thin  plates  which  cover 
the  cartilages  and  arch  over  the  spaces  between  them.  A  few 
cartilage  bones  are  present,  however,  in  the  hinder  part  of  the 
skull. 

The  bones  and  cartilages  of  the  cranium  may  be  divided 
into  two  groups,  —  (a)  those  forming  the  cranium  proper,  or 
brain  case,  and  (b)  those  forming  the  capsules  of  the  special 
sense  organs. 

The  cranium  proper  contains  the  following  bones.  Surround- 
ing the  foramen  magnum,  except  a  small  space  on  the  dorsal 
and  ventral  sides,  are  the  paired  exoccipital  bones.  They  are  car- 
tilage bones ;  the  remainder  of  the  occipital  region  does  not 
ossify  but  remains  cartilaginous.  Each  exoccipital  bears  on  its 
posterior  surface  an  articular  process  —  the  occipital  condyle  — 
by  which  the  skull  articulates  with  the  spinal  column.  Forming 
the  roof  of  the  cranium  are  two  pairs  of  large  membrane  bones, 
the  parietals  and  frontals.  The  parietals  extend  from  the  hinder 
end  of  the  skull  forward ;  the  frontals  overlap  the  anterior  pro- 
jections of  the  parietals  and  extend  almost  to  the  forward  end 
of  the  skull. 


90  VERTEBRATE  ZOOLOGY 

The  ventral  portion  of  the  cranium  proper  consists  of  a  single 
very  large  membrane  bone,  —  the  parasphenoid,  or  parabasal, — 
which  extends  from  the  hinder  almost  to  the  forward  end  of  the 
skull  and  forms  the  roof  of  the  mouth. 

Three  pairs  of  special  sense  capsules  are  present,  —  the  audi- 
tory, optic,  and  nasal. 

The  nasal  capsules  occupy  the  forward  end  of  the  skull.  Each 
capsule  is  an  elongated  space  which  opens  to  the  outside  by 
means  of  the  anterior  and  the  posterior  nares.  The  two  ante- 
rior nares  are  situated  at  the  forward  end  of  the  skull,  with 
a  wide  space  between  them;  the  posterior  nares  are  on  the 
under  surface,  at  the  hinder  end  of  the  capsule,  and  open  into 
the  mouth.  The  nasal  capsules  consist  largely  of  cartilage. 
The  only  bones  which  belong  to  them  are  a  pair  of  large  mem- 
brane bones,  —  the  vomers,  —  which  form  most  of  their  ventral 
surface.  These  bones  overlap  the  forward  end  of  the  parasphe- 
noid and  bear  teeth  along  their  anterior  edge ;  between  them 
in  the  midventral  area  will  be  seen  an  internasal  plate  of  car- 
tilage. The  roof  and  sides  of  the  nasal  capsules  are  formed  by 
a  delicate  fenestrated  cartilage  which  is  covered  above  by  the 
frontal  bones. 

The  optic  capsules  are  a  pair  of  very  delicate,  ring-shaped 
cartilages,  one  of  which  surrounds  the  eyeball  on  each  side, 
imbedded  in  its  sclera;  they  cannot  be  seen  in  a  dissection. 

The  auditory  capsules  are  a  pair  of  large,  globular  structures 
which  lie  at  the  hinder  end  of  the  skull,  one  on  each  side  of 
the  brain  case.  Each  capsule  consists  largely  of  cartilage  and 
is  partly  overlapped  by  the  lateral  edge  of  the  parietal  bone 
dorsally  and  by  that  of  the  parasphenoid  bone  ventrally. 

Three  cartilage  bones  are  present  in  each  capsule,  —  the  opis- 
thotic,  the  prootic,  and  the  operculum.  The  opisthotic  lies  at  the 
latero-posterior  corner  of  the  cranium  and  forms  the  hinder  end 
of  the  skull  at  this  place.  The  prootic  lies  directly  in  front  of 
but  not  in  contact  with  the  opisthotic,  and  forms  the  forward 
end  of  the  auditory  capsule ;  it  is  at  the  level  of  the  hinder 
end  of  the  frontal  bones.  Within  this  bone  is  the  membranous 
labyrinth  of  the  ear.  Both  of  these  bones  appear  on  both  the 


KECTURUS  91 

dorsal  and  the  ventral  side  of  the  skull  and  are  partly  covered 
by  the  parasphenoid  and  the  parietal  bones.  Between  these  two 
bones  on  the  ventral  side  of  the  skull  there  appears  a  small  round 
bone  —  the  operculum — which  exactly  fits  into  a  round  opening 
in  the  auditory  capsule  called  the  fenestra  ovalis ;  a  short  pro- 
jection of  this  bone  is  directed  forward  and  upward. 

Along  the  entire  outer  edge  of  the  auditory  capsule  is  a  flat 
membrane  bone,  called  the  paraquadrate,  or  squamosal,  from  the 
middle  of  which  a  short  projection  extends  to  the  operculum. 

The  remaining  bones  of  the  skull  belong  to  the  visceral  skele- 
ton and  may  be  divided  into  two  groups,  —  the  upper  jaw  and 
the  suspensorium  of  the  lower  jaw. 

The  upper  jaw  is  very  weak  in  Necturus.  In  the  typical 
amphibian  it  consists  of  two  distinct  arches,  an  outer  or  max- 
illary and  an  inner  or  palatopterygoid  arch;  in  the  frog  the 
arches  are  well  represented.  In  Necturus  they  are  present  only 
in  part.  The  outer  arch  is  represented  only  by  the  premax- 
illary  bones.  These  are  a  pair  of  V-shaped  membrane  bones 
which  form  the  anterior  end  of  the  skull  and  bear  the  ante- 
rior row  of  teeth.  Maxillary  and  jugal  bones  —  which  in  other 
amphibians  lie  back  of  these  and  complete  the  arch  —  are 
not  present.  The  inner  arch  is  represented  only  by  the  palato- 
pterygoid bones,  —  a  pair  of  large  membrane  bones  which  lie* 
immediately  back  of  the  vomers  and  bear  teeth  at  their  for- 
ward ends. 

The  suspensorium  is  formed  by  the  quadrate  cartilage,  the  quad- 
rate bone  which  develops  in  the  cartilage,  and  the  squamosal  or 
paraquadrate,  a  membrane  bone.  The  quadrate  bone  forms  the 
extreme  lateral  portion  of  the  skull;  its  anterior  face  is  the 
surface  with  which  the  lower  jaw  articulates.  The  quadrate 
cartilage  extends  medially  from  the  bone  to  the  cranium.  The 
paraquadrate,  as  we  have  already  seen,  lies  along  the  side  of  the 
skull,  extending  from  the  quadrate  bone  back  to  the  opisthotic. 

Extending  laterally  from  the  cranium  at  the  level  of  the 
forward  end  of  the  palatopterygoid  bone,  on  each  side,  is  a 
small  cartilage  called  the  anteorbital  cartilage ;  it  is  very  easily 
lost  in  the  preparation  of  the  skull. 


92  VERTEBRATE  ZOOLOGY 

Exercise  23.  Draw  the  dorsal  aspect  of  the  skull  on  a  scale  of  2, 
showing  accurately  the  outlines  of  the  bones  and  cartilages. 
Indicate  by  shading  the  cartilages,  cartilage  bones,  and 
membrane  bones. 

Exercise  24.  Draw  the  ventral  aspect  in  the  same  way. 

Boil  the  skull  until  the  bones  can  be  separated  from  one 
another  and  from  the  chondrocranium.  Carefully  observe  the 
extent  of  the  latter  and  its  relation  to  the  cartilage  and  the 
membrane  bones. 

The  vertebral  column  is  composed  of  about  forty-six  vertebrae. 
Four  regions  may  be  distinguished  in  it,  —  a  cervical  region, 
consisting  of  the  first  vertebra,  the  atlas ;  a  thoraco-lumbar 
region,  consisting  of  about  eighteen  vertebrae;  a  sacral  region, 
consisting  of  one  vertebra,  usually  the  nineteenth,  which  forms 
the  sacrum  and  supports  the  pelvis ;  and  a  caudal  region,  con- 
sisting of  the  remaining  vertebrae. 

A  typical  vertebra  is  made  up  of  the  following  parts :  a  cylin- 
drical centrum  or  body ;  a  flattened  neural  arch  on  the  dorsal  side 
of  the  centrum,  in  which  the  spinal  cord  lies ;  and  a  pair  of 
large,  irregular  transverse  processes  at  the  sides  of  the  centrum 
and  neural  arch  which  bear  the  ribs. 

Note  the  shape  of  the  centrum.  It  has  a  deep  depression  at 
each  end,  making  it  biconcave  or  amphicoelous,  which  is,  in  a 
fresh  condition,  filled  with  the  soft  notochord.  The  neural 
arch  is  made  up  of  a  pair  of  neural  processes,  —  which  form  the 
lateral  walls,  —  and  the  neural  spine,  which  forms  its  roof.  At 
each  end  of  the  neural  arch  is  a  pair  of  horizontally  flattened 
prolongations  called  zygapophyses,  by  means  of  which  the  verte- 
brae articulate  with  one  another. 

Study  the  regions  of  the  vertebral  column.  The  first  ver- 
tebra, which  forms  the  cervical  region,  is  called  the  atlas.  It  is 
about  half  as  long  as  those  immediately  behind  it,  and  has  very 
short  transverse  processes.  On  its  anterior  surface  is  a  pair 
of  depressions  into  which  the  occipital  condyles  of  the  skull  fit. 
The  thoraco-lumbar  vertebrae  are  the  largest  and  all  bear  ribs.  The 
sacral  vertebra,  which  is  usually  the  nineteenth,  is  similar  to  the 


NECTURUS  93 

thoraco-lumbar  in  size  and  form ;  its  transverse  processes  are, 
however,  somewhat  larger  and  its  ribs  longer  than  those  of 
the  other  vertebrae,  and  the  distal  ends  of  the  ribs  articulate 
with  the  pelvic  girdle.  The  caudal  vertebrae  vary  much  in  form 
and  size.  The  first  two  or  three  are  similar  to  those  of  the 
thoraco-lumbar  region,  but  are  smaller,  with  transverse  pro- 
cesses much  less  developed,  and  usually  without  ribs.  From 
about  the  twenty- third  vertebra  a  ventral  or  haemal  arch,  in 
which  the  caudal  vein  and  artery  lie,  characterizes  the  ventral 
side  of  the  vertebra. 

The  ribs  are  small,  rather  irregular  rods  of  bone,  which  are 
bifurcated  at  their  proximal  ends. 

Exercise  25.  Draw  three  views,  on  a  scale  of  2  or  3,  of  one  of 
the  thoraco-lumbar  vertebrae  and  the  ribs  belonging  to  it,  — 
an  anterior  view,  a  side  view,  and  a  ventral  view. 

Exercise  26.  Draw  the  anterior  end  of  the  atlas  on  a  scale  of 
2  or  3. 

Exercise  27.  Draw  an  anterior  and  also  a  side  view  of  the 
twenty-fourth  vertebra  on  a  scale  of  2  or  3. 


94  VEETEBEATE  ZOOLOGY 


AN  ANURAN  AMPHIBIAN.  THE  FROG 

The  Anura  are  the  tailless  Amphibia  and  include  the  frogs 
and  toads.  The  following  descriptions  will  enable  the  student 
to  identify  the  commonest  species  of  frogs.1 

Rana  virescens,  the  leopard  frog.  Green  or  brown,  with  large  black 
blotches  edged  with  white  or  yellow,  which  lie  in  two  irregular  rows  on  the 
back;  legs  barred  above  ;  belly  pearly  or  yellowish  ;  length  about  2£  inches; 
lives  in  marshes  and  wet  places. 

Rana  palustris,  the  pickerel  frog.  Brown  or  greenish,  with  several  rows 
of  oblong  square  blotcnes  on  back  and  sides ;  length  about  3  inches ;  com- 
mon in  cold  springs  or  streams  or  in  the  grass. 

Rana  clamala,  the  green  or  spring  frog.  Green  or  brown,  with  rounded 
spots  all  over  back ;  legs  with  several  cross  bands ;  beneath,  pure  white ; 
length  3  inches ;  lives  in  ponds  and  streams. 

Rana  catesliana,  the  bullfrog.  Green  or  brown,  with  faint  dark  spots 
above  ;  head  often  bright  green  ;  beneath,  with  pale  blotches  ;  length  5  to 
8  inches ;  lives  in  ponds  and  streams. 

Rana  sylvatica,  the  wood  frog.  Pale  reddish  brown;  head  small  and 
pointed  with  a  dark  band  on  each  side  between  eye  and  arm;  length 
1^  inches;  lives  in  the  woods  and  in  the  grass. 

Three  specimens  will  be  needed  for  a  complete  dissection  of 
the  frog, — one  for  the  outer  form  and  the  greater  part  of  the  inter- 
nal organs,  including  the  heart  and  the  great  blood  vessels  enter- 
ing and  leaving  it ;  one  for  the  blood  vessels ;  and  one  for  the 
skeleton.  The  animals  should  be  killed  as  needed  and  preserved 
during  the  dissection  in  a  five  per  cent  solution  of  formalin. 

Place  the  animal  (alive  if  possible)  under  a  glass  or  in  a  dissect- 
ing pan  and  observe  its  form  and  color.  The  body  is  short  and  com- 
pact, with  a  large  head  and  mouth;  the  hinder  end  is  characterized 
by  the  lack  of  a  tail  and  by  the  great  length  of  the  hind  legs.  The 
color  is  such  as  to  adapt  it  to  the  environment  in  which  it  lives, 
and  may  change  from  time  to  time,  like  that  of  a  chameleon. 

1  These  descriptions  have  been  modified  from  Bulletin  No.  51  of  the  New 
York  State  Museum  and  Jordan's  Manual  of  Vertebrates. 


THE  FROG  95 

The  skin  of  the  frog  is  without  scales  or  other  hardened 
integumentary  structures,  such  as  are  possessed  by  all  verte- 
brates except  the  urodelan  and  anuran  amphibians.  It  is,  how- 
ever, provided  with  numerous  integumentary  glands  which 
secrete  a  protective  slime.  The  characteristic  triradiate  openings 
of  these  glands  "may  be  seen  with  the  aid  of  a  hand  lens  in  skin 
which  the  frog  has  shed;  pieces  of  skin  will  often  be  found 
in  the  water  in  which  the  animals  have  been  kept. 

The  body  of  the  frog  may  be  divided  into  two  regions,  —  the 
head  and  the  trunk.  The  neck  region  —  which  is  wanting  in  fishes 
and  is  so  characteristic  of  land  vertebrates  —  is  just  beginning  to 
make  its  appearance  in  amphibians.  A  distinct  neck  is  not  pres- 
ent ;  there  is  present,  however,  one  cervical  vertebra  with  which 
the  skull  articulates.  The  caudal  region  is  also  wanting  in  adult 
anurans.  In  the  larval  frog  and  toad  a  long  tail  is  present,  by 
means  of  which  the  animal  swims ;  it  is,  however,  gradually 
absorbed  as  the  tadpole  passes  through  its  metamorphosis. 

The  head.  This  body  division  is  triangular  in  shape.  The 
mouth  is  large  and  bordered  by  skinny  lips,  which  close  tightly 
together  like  the  cover  on  a  box  and  thus  prevent. air  from 
escaping  during  the  act  of  respiration.  The  eyes  are  large  and 
protruding.  Each  is  protected  by  two  eyelids,  the  upper  one  of 
which  is  large  and  thick  and  with  little  power  of  movement ; 
the  lower  one  is  semitransparent  and  movable. 

In  front  of  the  eyes  are  the  nostrils,  or  anterior  nares  ;  each  of 
these  is  provided  with  a  valve  which  can  be  tightly  closed.  The 
nostrils  communicate  directly  with  the  mouth.  Probe  them  with 
a  bristle.  Back  of  each  eye  is  a  large  circular  area,  —  the  tympanic 
membrane,  or  ear  drum,  —  which  is  thus  on  the  outer  surface  of 
the  body.  Between  the  eyes  is  a  small  dark  spot  which  marks 
the  frontal  organ :  it  is  a  rudiment  of  a  median  eye.  In  the  male 
frog,  in  certain  species,  a  pair  of  large  vocal  sacs  projects  from 
the  hinder  part  of  the  head  in  the  breeding  season.  Probe  them 
from  the  mouth,  if  present. 

The  trunk.  This  body  division  is  short  and  shows  exter- 
nally no  marks  of  segmentation ;  it  bears  the  appendages.  In  the 
middle  of  the  back  will  be  noticed  a  prominent  hump,  which 


96  VEETEBEATE  ZOOLOGY 

indicates  the  position  of  the  sacrum,  where  the  hinder  append- 
ages articulate  with  the  spinal  column.  At  the  posterior  end  of 
the  trunk  and  slightly  dorsal  in  position  is  the  small  opening 
of  the  cloaca,  the  anus. 

The  appendages.  Two  pairs  of  legs  are  present:  each  leg  is 
made  up  of  three  divisions, — a  proximal,  a  middle,  and  a  distal 
division,  —  which  correspond  to  the  upper  arm,  the  forearm,  and 
the  wrist  -and  hand  respectively,  in  the  fore  leg,  and  in  the 
hind  leg  to  the  thigh,  the  shank,  and  the  ankle  and  foot.  The 
toes  have  no  claws. 

The  fore  legs  are  relatively  short  and  weak  and  do  not  aid  in 
locomotion.  Four  ringers  are  present,  the  thumb  being  rudi- 
mentary. In  the  male  frog  the  first  finger  is  thickened.  The 
fingers  are  not  joined  by  a  web. 

The  hind  legs  are  long  and  muscular  and  are  the  principal 
organs  of  locomotion  both  on  land  and  in  the  water.  While  the 
animal  is  at  rest  the  hind  legs  are  folded  together  back  of  it  in 
a  position  ready  for  springing.  In  this  position  the  three  divi- 
sions of  the  leg  become  apparent.  In  the  distal  division  certain 
ankle  bones  are  much  elongated  and  make  this  the  longest  of  the 
three  divisions.  The  five  toes  are  webbed, —  the  medial  (inner- 
most) one  being  the  big  toe. 

Exercise  i.  Draw  the  animal  as  it  sits  or  lies  before  you. 

If  the  animal  be  still  alive,  it  may  be  killed  by  placing  it  in  a 
jar  of  water  in  which  a  small  quantity  of  chloroform  or  ether 
has  been  put. 

Exercise  2.  Draw  a  dorsal  view  of  the  extended  animal,  showing 
the  features  above  mentioned;  carefully  label  all. 

Exercise  3.  Draw  a  side  view  of  the  head. 

The  mouth  and  pharynx.  Open  the  mouth  as  wide  as  possi- 
ble ;  cut  each  angle  of  the  jaw  a  little,  if  necessary,  so  that  the 
mouth  will  remain  open.  The  mouth  and  pharynx  will  be  seen 
to  be  a  single  space  which  extends  bac"k  to  the  beginning  of 
the  ossophagus.  With  forceps  pull  the  tongue  forward;  it  is  a 


THE  FROG  97 

slimy,  band  like  structure  which  is  attached  only  at  its  forward 
end.  The  hinder  end,  which  extends  back  into  the  pharynx, 
is  bilobed.  The  lower  jaw  is  without  teeth.  Just  back  of  the 
tongue  in  the  floor  of  the  mouth  may  be  felt  the  hyoid  cartilage, 
which  supports  the  tongue. 

Back  of  the  tongue  is  the  glottis,  — a  median  longitudinal  slit 
which  opens  into  the  lungs.  The  glottis  is  in  the  middle  of  an 
elliptical  elevation  formed  by  the  two  arytenoid  cartilages  ;  it  is 
usually  closed,  but  may  be  opened  with  a  needle.  Place  the 
end  of  a  blowpipe  in  it  and  blow  up  the  lungs. 

The  frog  has  two  methods  of  respiration,  —  first  with  the 
skin  and  the  mucous  membrane  of  the  mouth  and  pharynx, 
and  second  with  the  lungs.  Air  is  taken  by  regular  inspirations 
through  the  nostrils  into  the  mouth  and  pharynx,  where  it  is 
acted  upon  by  the  highly  vascular  mucous  membrane.  It  is  also 
at  irregular  intervals  taken  by  an  act  of  swallowing  through  the 
glottis  into  the  lungs.  It  is  expelled  from  the  lungs  by  the 
elasticity  of  their  walls  —  which  contain  muscle  fibers  —  and 
that  of  the  muscular  sides  of  the  body.  Immediately  after  the 
expiration  air  is  again  swallowed,  so  that  the  lungs  are  kept 
filled.  The  floor  of  the  mouth  will  be  observed  in  the  live  frog  to 
oscillate  rapidly  and  regularly.  This  act  is  not  connected  directly 
with  the  pulmonary  but  rather  with  the  pharyngeal  respiration. 

The  opening  behind  the  glottis  into  the  digestive  tract  is  the 
gullet,  or  oesophagus.  Probe  it. 

In  the  roof  of  the  mouth  note  the  upper  jaw,  in  which  is  a 
row  of  teeth  called  the  maxillary  teeth.  Just  behind  them  in  the 
forward  part  of  the  mouth,  near  the  median  line,  are  two  small 
groups  of  teeth  called  the  vomerine  teeth.  On  each  side  of  these 
is  one  of  the  paired  posterior  nares,  the  inner  openings  of  the 
nostrils.  Probe  them.  Near  the  angle  of  the  mouth  on  each 
side  is  the  large  opening  into  the  tympanic  cavity,  the  Eustachian 
tube.  Probe  one. 

Exercise  4.  Draw  a  sketch  of  the  opened  mouth  and  pharynx  on 
a  scale  of  about  2,  and  carefully  label  all  the  organs  above 
mentioned. 


98  VEETEBKATE   ZOOLOGY 

The  internal  organs.  Place  the  animal  on  its  back  in  a  dis- 
secting pan  containing  water,  with  its  head  away  from  you,  and 
pin  it  fast  with  a  large  pin  through  the  tip  of  the  jaw  and  one 
through  each  of  the  four  legs.  Raise  the  skin  of  the  belly  with 
forceps,  and  with  scissors  make  an  incision  in  it  along  the  mid- 
ventral  line  the  entire  length  of  the  body. 

Notice  the  looseness  of  the  skin  and  the  large  space  between 
it  and  the  underlying  muscles.  This  space  is  a  lymph  cavity. 
Note  carefully  the  points  where  the  skin  is  attached  to  the  mus- 
cles. Note  the  large  blood  vessels  on  the  inner  surface  of  the 
skin :  these  are  the  cutaneous  veins  and  arteries.  The  blood  is 
brought  to  the  skin  to  be  aerated,  an  important  part  of  the  respi- 
ration of  the  animal  being  carried  on  through  the  skin. 

Through  the  semitransparent  muscles  in  the  region  of  the 
fore  legs  may  be  seen  and  felt  a  number  of  platelike  bones  and 
cartilages.  These  form  the  pectoral  (shoulder)  girdle  and  the 
breastbone,  which  support  the  fore  limbs.  In  the  midventral 
line  will  be  seen  through  the  body  wall  a  broad  dark  line :  it  is 
the  abdominal  vein. 

Observe  the  arrangement  of  the  ventral  body  muscles ;  see 
page  122. 

Lift  up  the  ventral  body  wall  with  forceps,  and  with  scissors 
make  a  longitudinal  incision  through  it  in  the  median  line  the 
length  of  the  body.  Pull  the  two  flaps  of  the  body  wall  gently 
apart  and  pin  them.  Examine  the  organs  which  lie  in  the  ab- 
dominal cavity,  but  without  disturbing  any  of  them. 

If  the  animal  be  a  male  or  a  female  which  is  not  breeding, 
the  most  conspicuous  organs  will  be  the  large  reddish  liver  and 
the  intestine.  If  it  be  a  mature  female,  the  dark-colored  granular 
ovaries  may  occupy  a  large  part  of  the  space  within  the  body 
cavity ;  in  this  case  the  ovaries  should  be  removed  so  that  the 
other  organs  can  be  studied. 

Lying  on  the  left  side  of  the  liver  and  wholly  or  partly  con- 
cealed by  it  is  the  elongated  stomach.  In  front  of  the  liver  in  the 
median  line  is  the  conical  heart  within  its  membranous  pericar- 
dium. Lying  between  the  lobes  of  the  liver  may  be  seen  the 
small  greenish,  spherical  gall  bladder. 


THE  FEOG  99 

Make  a  transverse  incision  in  each  flap  of  the  body  wall. 
Turn  the  flaps  to  the  side  and  pin  them  down,  exposing  fully 
the  internal  organs. 

In  addition  to  the  organs  already  mentioned  one  or  both  lungs 
may  be  seen.  They  are  usually  shriveled,  saclike  organs  which 
lie  at  the  forward  end  of  the  abdominal  cavity,  concealed  by  the 
liver.  If  either  be  full  of  air,  it  should  be  punctured  and  made 
to  collapse.  At  the  hinder  end  of  the  abdominal  cavity,  between 
the  base  of  the  hind  legs,  the  large  urinary  bladder  will  be  seen ; 
if  it  is  not  found  readily,  insert  the  blowpipe  in  the  anus  and 
inflate  the  bladder.  Several  elongated  yellowish  bodies  may  be 
seen  here  projecting  from  between  the  other  organs:  they  are 
called  the  fat  bodies. 

The  body  cavity  is  divided  into  two  compartments,  —  the  abdom- 
inal cavity  and  the  pericardial  cavity.  The  former  is  by  far  the 
larger  of  the  two  and  contains  the  liver,  intestine,  and  most  of 
the  other  viscera;  it  is  lined  by  a  membrane  called  the  perito- 
neum. The  pericardial  cavity  is  small,  being  only  large  enough 
to  contain  the  heart  and  the  base  of  the  great  blood  vessels ;  it 
is  formed  by  a  membrane  called  the  pericardium.  Note  that  the 
organs  in  the  abdominal  cavity  are  attached  to  the  walls  or  to 
each  other  by  thin  membranes.  These  are  the  mesenteries.  They 
are  folds  of  the  peritoneum  and  have  come  into  existence  as  a 
result  of  the  growth  of  these  organs  in  the  body  cavity.  The 
peritoneum  is  a  closed  sac  with  extensive  mesenterial  folds 
extending  into  it,  within  which  lie  the  various  organs. 

Exercise  5.  Draw  an  enlarged  outline  of  the  animal  and  in  it  the 
internal  organs  as  they  lie  in  the  body  cavity  before  they 
have  been  disturbed;  label  all  carefully. 

The  digestive  system.  This  system  consists  of  the  mouth, 
pharynx,  oasophagus,  stomach,  intestine,  cloaca,  liver,  and  pan- 
creas. 

The  mouth  and  pharynx  have  already  been  studied.  Without 
cutting  anything,  press  the  liver  to  the  animal's  right  and  fully 
expose  the  stomach.  It  will  be  seen  to  be  a  large,  curved  organ, 
the  anterior  or  cardiac  end  being  near  the  left  lung  at  the  side  of 


100  VERTEBRATE  ZOOLOGY 

the  heart,  and  the  posterior  or  pyloric  end  being  near  the  median 
line  of  the  body.  The  oesophagus  is  a  short  tube,  not  quite  as 
wide  as  the  stomach,  which  joins  the  cardiac  end  of  that  organ 
with  the  pharynx. 

From  the  pyloric  end  of  the  stomach,  which  is  marked  by 
a  constriction,  the  intestine  proceeds,  with  many  turns,  to  the 
hinder  part  of  the  body.  It  is  composed  of  two  divisions,  —  the 
small  intestine,  and  the  large  intestine  or  rectum.  The  small  intes- 
tine forms  the  greater  part  of  it.  Its  anterior  portion  —  the  duo- 
denum —  is  bent  forward  so  as  to  lie  parallel  with  the  stomach, 
and  between  them  lies  the  whitish,  irregularly  shaped  pancreas. 
The  rectum  is  about  half  an  inch  long  and  forms  the  hinder 
part  of  the  intestine ;  it  is  much  wider  than  the  small  intestine 
and  may  often  be  recognized  by  its  dark  color.  The  rectum  is 
continuous  posteriorly  with  the  cloaca,  —  a  short,  wide  vessel 
which  lies  between  the  base  of  the  hind  legs  and  finds  an  outlet 
through  the  anus. 

Observe  again  the  extensive  mesenteries  which  bind  the  divi- 
sions of  the  digestive  tract  with  the  wall  of  the  abdominal 
cavity. 

At  one  side  of  the  forward  portion  of  the  rectum  will  be 
seen  a  dark-red  spherical  body,  —  the  spleen.  Press  the  intestine 
and  mesentery  aside, — but  without  cutting  them, — and  observe 
the  flattened,  dark-colored  kidneys,  which  lie  close  to  the  dorsal 
body  wall.  At  their  forward  ends  are  the  two  yellow,  spherical 
testes,  —  if  the  animal  be  a  male,  —  or  the  irregular,  saclike 
ovaries  if  a  female,  while  in  front  of  these  organs  are  the  yellow, 
finger-shaped  fat  bodies. 

Observe  closely  the  liver  and  pancreas.  The  former  is  com- 
posed of  two  main  lobes,  one  of  which  is  subdivided  into  two 
smaller  lobes.  Note  carefully  the  connection  between  these 
two  parts.  Turn  the  whole  liver  forward,  —  but  without  cutting 
anything,  —  pin  it  there,  and  study  its  dorsal  surface  and  the 
pancreas. 

The  pancreas  is  an  irregular,  whitish  gland  which  lies  in  the 
bend  made  by  the  stomach  and  the  duodenum.  Near  the  hinder 
border  of  the  liver  note  the  spherical  gall  bladder.  Find  the  bile 


THE  FKOG  101 

duct,  which  joins  the  liver  with  the  duodenum.  It  is  a  slender 
tube  which  issues  from  the  gall  bladder  and,  after  receiving  a 
number  of  branch  ducts  from  the  liver,  joins  the  duodenum  a 
short  distance  from  the  pylorus.  It  passes  through  the  pan- 
creas, from  which  it  receives  one  or  more  small  pancreatic  ducts. 
Gently  squeeze  the  gall  bladder  with  forceps  and  force  the  dark- 
green  bile  into  the  duct ;  it  will  thus  be  easy  to  follow.  If  the 
bile  will  not  flow,  cut  the  gall  bladder  open  and  inject  a  carmine 
solution  in  it  with  a  pipette. 

Exercise  6.  Make  a  semidiagrammatic  drawing  of  the  dorsal 
surface  of  the  liver  and  pancreas,  with  an  outline  of  the 
stomach  and  duodenum,  showing  the  features  just  described; 
carefully  label  all  the  organs. 

The  study  of  the  digestive  system  will  be  completed  after 
the  heart  has  been  examined. 

The  heart  and  its  vessels.  The  heart  of  the  frog  is  composed 
of  five  divisions,  —  a  single  ventricle,  two  auricles,  the  sinus 
venosus,  and  the  truncus  arteriosus.  Observe  the  pericardium, 
which  closely  invests  the  heart. 

The  ventricle  is  the  large  conical  posterior  portion  of  the  heart ; 
by  its  contractions  the  blood  is  sent  forward  through  the  trun- 
cus arteriosus,  which  is  the  large  cylindrical  vessel  springing 
from  its  anterior  end.  The  truncus  is  made  up  of  two  por- 
tions, —  a  basal  portion,  which  is  called  the  bulbus  cordis,  and 
an  anterior  portion.  The  latter  at  once  divides  into  two  large 
vessels  which  pass  forward  and  leave  the  pericardial  space. 
Each  of  these  vessels  then  divides  into  three  arteries,  called  the 
aortic  arches,  through  which  the  blood  is  carried  to  all  parts  of 
the  body.  The  anterior  arch  is  called  the  carotid  arch ;  it  carries 
blood  to  the  head.  The  middle  arch  is  called  the  systemic  arch. 
The  right  and  left  sides  of  this  arch  meet  back  of  the  heart 
and  form  the  aorta  descendens,  or  dorsal  aorta,  which  lies  just  beneath 
the  spinal  column  and  distributes  arterial  blood  to  the  trunk 
and  extremities.  The  posterior  arch  is  the  pulmocutaneous  arch; 
through  it  blood  is  carried  to  the  lungs  and  the  skin  for 
aeration. 


102  VERTEBRATE  ZOOLOGY 

In  front  of  the  ventricle  are  the  right  and  left  auricles ;  they 
appear  dark  colored  in  consequence  of  the  thinness  of  their 
walls.  On  the  dorsal  side  of  the  heart  is  a  large,  thin-walled, 
dark-colored  sac,  —  the  sinus  venosus.  Blood  is  brought  to  the 
heart  from  the  organs  and  tissues  of  the  body  by  three  large 
veins  which  enter  the  sinus  venosus :  these  are  the  right  and 
left  precaval  veins,  which  enter  the  forward  end  of  the  sinus,  bring- 
ing blood  from  the  forward  part  of  the  body ;  and  the  postcaval 
vein,  which  enters  the  hinder  end  of  the  sinus,  bringing  blood 
from  the  hinder  part  of  the  body.  From  the  sinus  the  blood 
enters  the  right  auricle.  Blood  is  brought  to  the  heart  from 
the  lungs  by  the  pulmonary  vein,  which  lies  alongside  the  left 
precaval  vein  and  enters  the  left  auricle ;  this  vein  is  formed 
by  the  union  of  a  right  and  a  left  pulmonary  vein  which  bring 
blood  from  the  two  lungs. 

Exercise  7.  Make  a  drawing  of  the  ventral  aspect  of  the  heart 
and  the  blood  vessels,  so  far  as  these  have  been  observed, 
on  a  scale  of  2  or  3. 

Bend  the  ventricle  forward  and  study  its  dorsal  aspect. 
Identify  the  sinus  venosus,  the  three  caval  and  the  pulmonary 
veins. 

Exercise  8.  Make  a  drawing  of  the  dorsal  aspect  of  the  heart 
on  a  scale  of  2  or  3. 

The  internal  structure  of  the  heart.  Cut  the  aortic  arches 
and  the  caval  veins  and  remove  the  heart  from  the  body.  Place 
it  in  a  small  dish  of  water  with  the  dorsal  side  uppermost, 
Identify  the  stumps  of  the  three  caval  veins  and  the  pulmonary 
vein.  Cut  off  the  dorsal  wall  of  the  sinus  venosus  and  wash 
the  blood  from  its  cavity.  Note  the  opening  into  the  right 
auricle ;  if  it  is  not  easily  seen,  use  the  blowpipe. 

Place  the  ventral  surface  of  the  heart  uppermost ;  cut  away 
the  ventral  wall  of  the  two  auricles  and  wash  the  blood  from 
their  cavities.  Note  the  thin  septum  which  separates  the  right 
from  the  left  auricle. 


THE  FEOG  103 

In  the  right  auricle,  which  is  the  larger  of  the  two,  note  the 
opening  into  the  sinus  venosus,  near  the  septum ;  also  note  the 
muscular  ridges  on  its  inner  surface.  In  the  left  auricle  note 
the  small  opening  of  the  pulmonary  vein,  also  near  the  septum, 
and  the  muscular  ridges. 

Remove  the  ventral  wall  of  the  ventricle  and  expose  its 
cavity.  Note  the  smallness  of  its  cavity,  its  thick  walls,  and 
the  longitudinal  muscular  ridges  on  its  inner  surface  which 
divide  the  cavity  into  compartments. 

The  presence  of  these  elongated  compartments  is  important 
inasmuch  as  they  prevent  the  complete  mixing  of  the  venous  and 
the  arterial  blood  which  would  otherwise  take  place.  Since  the 
ventricle  consists  of  a  single  chamber  into  which  both  kinds  of 
blood  are  poured  from  the  auricles,  it  would  contain  an  equal 
mixture  of  these  if  the  blood  could  flow  unimpeded  from  one 
part  of  the  ventricle  to  another.  As  it  is,  venous  blood  from 
the  right  auricle  goes  into  the  compartments  on  the  right  side 
of  the  ventricle,  and  the  more  nearly  arterial  blood  from  the 
left  auricle  goes  into  those  on  the  left  side,  and  but  a  slight 
mixing  of  the  blood  probably  takes  place. 

At  the  forward  end  of  the  ventricle  is  the  auriculo-ventricular 
opening,  which  leads  into  the  ventricle  from  both  auricles.  The 
septum  between  the  auricles  divides  this  opening  into  two  pas- 
sages, one  of  which  leads  from  each  auricle.  This  opening  is 
guarded  by  a  semilunar  valve  extending  into  the  ventricle,  to  the 
dorsal  wall  of  which  it  is  attached  by  tendinous  cords.  Look 
for  them  with  the  aid  of  the  blowpipe. 

At  the  forward  end  of  the  ventricle,  also,  to  the  right,  is  the 
opening  into  the  truncus  arteriosus.  It  is  guarded  by  three  semi- 
lunar  valves.  Look  for  them  with  the  aid  of  the  blowpipe. 

The  space  in  the  truncus  is  incompletely  divided  into  two 
compartments  by  a  large  longitudinal  ridge  springing  from  its 
dorsal  wall  which  is  called  the  spiral  valve.  Of  these  compart- 
ments the  right-hand  one  may  be  called  the  arterial  compartment, 
and  the  left-hand  one  the  pulmocutaneous  compartment.  Note 
carefully  the  shape  of  the  spiral  valve  and  its  relation  to  the 
opening  into  the  ventricle. 


104  VEETEBEATE  ZOOLOGY 

At  the  forward  end  of  the  spiral  valve  are  three  additional 
pouch-shaped  valves.  The  one  of  these  on  the  right  side  is  the 
anterior  end  of  the  spiral  valve ;  it  is  the  largest  of  the  three. 
The  other  two  are  one  on  the  left  and  one  on  the  dorsal  side 
of  the  truncus  and  are  much  smaller.  These  things  are  difficult 
to  see  except  in  a  large  frog. 

Make  a  cross  section  of  one  of  the  two  branches  of  the 
truncus  and  note  that  it  is  divided  by  longitudinal  partitions 
into  three  chambers  which  communicate  with  the  three  aortic 
arches.  Probe  these  chambers.  The  innermost  or  anterior  cham- 
ber takes  blood  to  the  carotid  artery,  the  middle  chamber  takes 
it  to  the  systemic  artery,  and  the  outer  or  posterior  chamber 
takes  it  to  the  pulmocutaneous  artery.  Note  that  the  pulmo- 
cutaneous  chambers  on  the  two  sides  meet  and  open  posteriorly 
through  a  single  aperture  at  the  anterior  end  of  the  pulmocu- 
taneous compartment  of  the  truncus,  which  has  received  venous 
blood  from  the  ventricle.  The  arterial  compartment  which  has 
received  arterial  blood  delivers  it  to  the  carotid  and  systemic 
arches. 

It  will  be  seen  that  the  purpose  of  this  arrangement  is  to 
effect  such  a  division  of  the  blood  that  the  pulmocutaneous 
arch  will  receive  principally  venous  blood,  which  it  takes  to 
the  lungs  and  the  skin  to  be  purified,  while  the  more  nearly 
arterial  blood  comes  into  the  carotid  and  systemic  arches  and  is 
distributed  throughout  the  body. 

Exercise  9.  Draw  a  diagrammatic  sketch  of  the  heart  with  the 
ventral  wall  removed,  showing  these  features. 

The  digestive  system  (continued).  Take  out  this  system  in  the 
following  way.  Lift  up  the  liver  with  forceps,  and  with  scissors 
free  its  anterior  border  from  the  tissues  beneath  it,  being  careful 
not  to  injure  the  lungs.  Find  the  oesophagus,  which  joins  the 
stomach  with  the  pharynx.  Note  that  the  lungs  also  join  the 
ventral  wall  of  the  pharynx.  Take  hold  of  the  oesophagus  with 
forceps,  lift  it  up,  and  with  scissors  cut  across  the  floor  of  the 
mouth  in  front  of  the  lungs. 


THE  FBOG  105 

The  forward  end  of  the  digestive  tract,  with  the  lungs,  being 
thus  cut  loose  from  the  body,  can  be  bent  backward.  With 
scissors  cut  the  stomach  and  liver  loose  from  the  tissues  beneath 
them;  cut  the  mesentery  by  which  the  intestine  is  joined  with 
the  dorsal  body  wall,  being  careful  not  to  injure  the  flattened 
kidneys  and  testes  or  ovaries,  and  straighten  the  intestine  out. 
The  entire  digestive  tract,  together  with  the  lungs,  will  thus  be 
removed  from  the  body,  except  at  its  hinder  end.  Extend  it  in 
the  water  and  pin  it  there,  with  the  lungs  attached  to  the  pharynx, 
and  the  liver  and  pancreas  attached  to  the  duodenum  by  the 
bile  duct. 

Exercise  10.  Make  a  drawing  of  the  digestive  system,  with  the 
lungs ;  label  all  the  parts  and  organs  belonging  to  it. 

Slit  open  the  stomach  and  the  forward  end  of  the  intestine 
and  note  the  ridges  on  their  inner  surface.  Cut  open  a  lung 
and  note  that  it  is  a  hollow  sac  with  a  network  of  ridges  on 
the  inner  surface. 

The  urogenital  system.  The  urinary  and  the  genital  organs 
are  in  close  union  with  each  other,  notwithstanding  their  differ- 
ence in  function,  and  are  conveniently  studied  together.  The 
urinary  organs  consist  of  the  paired  kidneys,  the  paired  excurrent 
canals  or  Wolffian  ducts,  the  urinary  bladder,  and  the  cloaca. 

The  kidneys  are  two  large,  flattened  bodies  which  lie  close  to 
the  dorsal  body  wall  in  the  posterior  portion  of  the  body  cavity. 
Each  kidney  is  made  up  of  a  mass  of  fine  tubules,  each  of  which 
opens  into  the  body  cavity  at  one  end,  while  the  other  end  com- 
municates with  the  Wolffian  duct.  This  duct  acts  as  a  ureter. 
It  is  a  straight  white  tube  which  runs  from  the  outer  border  of 
the  kidney  to  the  dorsal  wall  of  the  cloaca.  The  urinary  bladder 
is  a  large,  bilobed  sac  at  the  hinder  end  of  the  body  cavity 
which  springs  from  the  ventral  wall  of  the  cloaca.  Its  opening 
into  the  cloaca  can  be  applied  closely  to  the  openings  of  the 
Wolffian  ducts  and  it  can  thus  receive  the  urine  from  them. 

On  the  ventral  surface  of  each  kidney  is  an  irregular,  yellow« 
ish  line  which  is  called  the  adrenal  body ;  its  function  is  unknown. 


106  VEETEBEATE   ZOOLOGY 

Examine  the  ventral  surface  of  the  kidney  with  a  hand  lens 
and  note  the  minute  openings  of  the  urinary  tubules. 

The  genital  organs  consist  of  the  testes  in  the  male  and  the 
ovaries  in  the  female,  and  the  ducts  which  conduct  the  genital 
products  to  the  outside. 

The  male.  The  testes  are  two  yellow,  ovoid  bodies  which  lie 
against  the  ventral  surface  of  the  kidneys  and  are  attached  to 
the  dorsal  wall  of  the  abdominal  cavity  by  mesenteries.  Join- 
ing each  testis  with  the  ventral  side  of  the  kidney  are  about  a 
dozen  fine  tubules,  the  vasa  efferentia,  which  are  suspended  in  the 
mesentery.  Through  these  the  spermatozoa,  which  are  formed 
in  the  testis,  make  their  way  into  the  kidney  and  thence  into 
the  Wolffian  duct.  This  duct  thus  serves  the  double  function 
of  a  ureter,  an  outlet  for  the  urine,  and  a  vas  deferens,  an  out- 
let for  sperm;  it  has  on  this  account  received  a  special  name 
and  is  called  Leydig's  duct.  It  is  only  in  elasmobranchs  and 
amphibians  that  Leydig's  duct  is  present.  Along  the  hinder 
end  of  this  duct  and  connected  with  it  by  ducts  is  the  seminal 
vesicle,  —  a  glandular  body  in  which  sperm  is  stored  during  the 
'breeding  season. 

The  female.  The  ovaries  differ  very  much  in  size  and  appear- 
ance at  different  times  of  the  year.  In  the  springtime  they  are 
often  so  distended  with  the  small,  spherical  ova  that  they  may 
almost  fill  the  abdominal  cavity.  If  this  is  not  their  condition, 
they  appear  as  a  pair  of  folded,  dark-colored  bodies  which  lie 
on  the  ventral  surface  of  the  kidneys  attached  to  the  dorsal 
body  wall  by  median  mesenteries.  The  paired  ducts  through 
which  the  -ova  find  their  way  to  the  cloaca  are  the  oviducts,  or 
Miillerian  ducts.  In  adult  females  each  of  these  ducts  is  a  thick- 
walled,  twisted  tube  which  lies  in  the  abdominal  cavity  against 
the  dorsal  body  wall.  Its  anterior  end  opens  into  this  cavity 
and  is  situated  at  the  side  of  the  heart,  while  the  posterior  end 
opens  into  the  cloaca.  The  posterior  portion  of  the  oviduct  is 
expanded  and  forms  a  uterus,  a  reservoir  for  ova. 

The  ova  escape  from  the  ovaries  by  the  rupture  of  their  walls 
into  the  abdominal  cavity;  they  then  make  their  way  to  the 
mouths  of  the  oviducts  and  through  them  into  the  cloaca. 


THE  FROG  107 

During  this  descent  of  the  ova  the  albumen  which  surrounds  it 
is  secreted  by  the  walls,  of  the  oviducts. 

At  the  anterior  end  of  the  kidneys  is  a  pair  of  prominent, 
yellow,  branching  fat  bodies.  They  are  lymphoid  bodies,  and 
vary  much  in  size  at  different  times  of  the  year,  being  largest 
before  the  breeding  season  and  smallest  after  it. 

While  studying  the  urogenital  system,  the  organs  of  which  it 
is  composed  need  not  be  disturbed.  With  a  strong  scalpel  cut 
through  the  bony  pelvis  exactly  in  the  median  line  between  the 
legs  in  order  to  expose  the  cloaca.  The  urinary  bladder  is  a 
delicate  structure  which  is  attached  to  the  body  wall  by  mesen- 
teries. It  must  be  freed  from  these  and  great  care  taken  not  to 
cut  either  it  or  the  cloaca. 

Slit  open  the  cloaca  along  the  side  and  find  the  mouth  of  the 
urinary  bladder.  Search  with  the  blowpipe  for  the  openings  of 
the  urogenital  ducts. 

Exercise  11.  Make  a  semidiagrammatic  drawing  of  the  urogenital 
system  with  the  cloaca;  label  carefully  all  its  parts. 

The  nervous  system.  This  system  is  made  up  of  the  follow- 
ing divisions:  (1)  the  central  nervous  system,  which  is  composed 
of  the  brain  and  the  spinal  cord ;  (2)  the  peripheral  nervous  system, 
which  is  composed  of  (a)  the  paired  cranial  and  spinal  nerves 
and  (b)  the  sympathetic  nervous  system ;  and  (3)  the  special  sense 
organs. 

The  cranial  nerves  and  the  spinal  nerves  each  number  ten 
pairs ;  the  former  spring  from  the  brain  and  the  latter  from  the 
spinal  cord  and  place  these  structures  in  communication  with 
the  various  organs  and  tissues  of  the  body.  The  sympathetic 
nervous  system  lies  in  the  body  cavity  in  connection  with  the 
cranial  and  spinal  nerves  and  innervates  certain  important 
viscera. 

Remove  the  urogenital  system  from  the  body.  Raise  it  care- 
fully with  forceps,  and  with  fine  scissors  cut  it  loose  from  the 
dorsal  body  wall.  Note  the  spinal  column  projecting  into  the 
body  cavity,  and  lying  ventral  to  it  note  a  large  blood  vessel,  — 


108  VEBTEBRATE   ZOOLOGY 

the  dorsal  aorta ;  this  must  not  be  disturbed.  The  spinal  column 
is  made  up  of  nine  vertebra  and  a  long  terminal  bone  called 
the  urostyle.  Identify  them. 

We  shall  study  first  the  spinal  nerves  and  the  sympathetic  system. 
Each  spinal  nerve  is  joined  with  the  spinal  cord  by  two  roots,  — 
a  dorsal  and  a  ventral  root,  —  and  passes  out  from  the  neural 
canal  of  the  spinal  column  through  a  space  between  two  verte- 
brae called  the  intervertebral  foramen.  At  the  point  where  these 
two  roots  meet,  the  dorsal  root  bears  a  large  ganglion  called  the 
spinal  ganglion.  This  ganglion  is  imbedded  in  a  prominent  white 
body  present  between  the  vertebrae  called  the  calcareous  body. 

The  ten  pairs  of  spinal  nerves  will  be  seen  in  the  body  cavity, 
where  they  appear  as  white  strands  which  lie  against  the  dorsal 
body  wall  on  each  side  of  the  vertebral  column.  The  most  con- 
spicuous ones  are  the  seventh,  eighth,  and  ninth  nerves,  which 
lie  close  together  in  the  hinder  part  of  the  abdominal  cavity. 
They  emerge  on  each  side  from  the  intervertebral  foramina, 
between  the  seventh  and  eighth  vertebrae,  the  eighth  and  ninth, 
and  the  ninth  and  the  urostyle  respectively,  and  proceed  straight 
back  almost  parallel  with  the  spinal  column.  These  nerves  are 
joined  with  one  another  by  short  connecting  branches  and  form 
a  network  or  plexus  called  the  sciatic  plexus.  From  this  plexus 
issue  a  number  of  nerves  which  proceed  to  the  hinder  quarters 
of  the  body  and  the  hind  legs.  Of  these  the  largest  are  the  sciatic 
nerve,  which  goes  to  the  hind  leg,  and  the  crural  and  iliohypogas- 
tric  nerves,  which  supply  the  muscles  and  skin  of  the  abdomen 
and  thigh. 

Find  the  sciatic  plexus  and  these  nerves.  Follow  the  sciatic 
nerve  into  the  leg ;  trace  the  other  two  as  far  as  possible. 

In  the  forward  part  of  the  abdominal  cavity,  on  each  side,  is 
another  nerve  plexus  called  the  brachial  plexus,  which  is  composed 
of  the  first  three  spinal  nerves.  Of  these  the  second,  which  is 
the  largest  and  most  conspicuous,  is  a  large  white  cord  lying  at 
right  angles  to  the  spinal  column  and  emerging  from  between 
the  second  and  third  vertebrae ;  it  is  joined  by  a  small  branch 
from  the  first  and  one  from  the  third  spinal  nerves,  and  passes 
to  the  fore  leg. 


THE  FEOG  109 

The  fourth,  fifth,  and  sixth  pairs  of  spinal  nerves  are  delicate 
cords  which  emerge  from  between  the  fourth  and  fifth,  fifth  and 
sixth,  and  sixth  and  seventh  vertebrae,  and  pass  obliquely  back- 
ward to  the  muscles  of  the  back. 

Find  these  nerves  and  trace  their  branches. 

The  sympathetic  system  consists  of  a  pair  of  delicate  longitudi- 
nal nerves  which  lie  in  the  abdominal  cavity  oil  either  side  of  the 
spinal  column,  close  to  the  dorsal  body  wall.  In  each  longitud- 
inal nerve  are  ten  enlargements, — the  sympathetic  ganglia, — from 
each  of  which  one  or  more  short  branches  run  to  a  spinal  nerve. 

The  first,  second,  and  third  of  these  ganglia  lie  close  to  the 
first,  second,  and  third  spinal  nerves  and  are  joined  with  them 
by  short  branches.  The  fourth  to  the  ninth  sympathetic  gan- 
glia, inclusive,  are  situated  nearer  the  median  plane  than  the 
first  three ;  they,  together  with  the  longitudinal  nerve,  lie  along- 
side the  dorsal  aorta,  which  will  be  noticed  as  a  median,  dark- 
colored  tube.  The  fourth  sympathetic  ganglion  is  the  smallest; 
the  ninth  is  the  largest  and  is'  joined  with  the  ninth  spinal 
nerve  by  several  branches ;  the  tenth  is  small  and  is  often 
wanting. 

Branches  from  the  sympathetic  nerves  and  their  ganglia  pass 
to  the  various  viscera.  The  largest  of  these  branches  proceed 
from  the  fourth,  fifth,  and  sixth  ganglia,  and  after  joining 
together  form  a  large  nerve  called  the  splanchnic  nerve,  which 
supplies  the  intestine  and  other  viscera. 

Study  the  sympathetic  system  ;  first  find  the  longitudinal 
nerves  and  ganglia,  then  observe  their  relations  to  the  spinal 
nerves  and  ganglia. 

Exercise  12.  Make  a  semidiagrammatic  drawing  of  the  spinal 
nerves  and  the  sympathetic  system.  Draw  first  an  outline 
of  the  spinal  column  as  it  appears  in  the  ventral  aspect  of 
the  opened  body  cavity;  number  the  vertebrae ;  draw  the 
spinal  nerves  and  then  the  sympathetic  system. 

The  brain  and  the  spinal  cord.  In  order  to  expose  these  organs 
remove  the  skin  and  muscles  from  the  back  of  the  head  and 
trunk.  Find  the  juncture  of  the  skull  with  the  backbone.  By 


110  VERTEBRATE   ZOOLOGY 

bending  the  head  slightly  down,  a  space  about  an  eighth  of  an 
inch  long,  which  is  covered  by  a  dark-colored  membrane,  may 
be  made  to  appear  between  the  skull  and  the  backbone.  With 
a  needle  very  carefully  remove  this  membrane ;  beneath  will  be 
seen  the  white  brain ;  this  must  not  be  injured.  Introduce  one 
blade  of  the  scissors  into  the  skull  through  the  opening,  and 
make  a  cut  along  the  side  of  the  skull  between  the  eyes.  Make 
a  similar  cut  along  the  other  side,  and  with  the  forceps  lift  off 
the  roof  of  the  skull,  thus  exposing  the  brain.  Similarly  cut 
through  the  two  sides  of  the  neural  canal,  which  contains  the 
spinal  cord,  and  expose  it. 

Carefully  remove  the  dark  membrane  which  covers  the  brain, 
and  observe  its  five  regions,  —  the  cerebrum,  the  thalamencepha- 
lon,  the  optic  lobes  or  midbrain,  the  cerebellum,  and  the  medulla 
oblongata. 

The  brain  and  spinal  cord  are  hollow  structures.  A  delicate 
canal,  called  the  central  canal,  runs  through  the  center  of  the 
cord;  in  the  brain  this  canal  widens  out  into  a  number  of 
spaces  which  are  called  the  ventricles. 

The  anterior  and  largest  region  of  the  brain  is  the  cerebrum. 
It  is  made  up  of  the  two  lateral  hemispheres,  which  are  separated 
from  each  other  by  the  sagittal  fissure.  The  anterior  ends  of  the 
hemispheres  are  fused  and  form  the  olfactory  lobe,  from  the  ante- 
rior end.  of  which  the  two  olfactory  nerves  pass  to  the  nose. 

Back  of  the  cerebrum  is  the  inconspicuous  thalamencephalon, 
and  behind  that  are  the  paired  optic  lobes,  or  midbrain.  In 
the  roof  of  the  thalamencephalon  will  be  seen,  with  the  aid 
of  the  lens,  several  delicate  structures.  Near  the  center  of  it 
arises  a  threadlike  projection  called  the  pineal  body,  or  epiphysis, 
which  extends  forward  over  the  thalamencephalon.  In  an  early 
period  of  the  larval  life  of  the  frog  the  epiphysis  extends 
through  the  skull  to  the  skin  on.  the  top  of  the  head  between 
the  eyes,  where  it  joins  the  brown  spot  known  as  the  frontal 
organ,  which  is  the  rudiment  of  the  pineal  eye;  this  connection 
is  lost  before  the  animal  becomes  adult. 

In  front  of  the  epiphysis  and  between  the  hinder  ends  of  the 
hemispheres  is  the  much  larger  paraphysis,  a  dark-colored,  vascular 


t    r     * 

THE  FEOG  HI 

body  extending  up  to  the  skull.  At  its  base  and  partly  con- 
cealed by  it  is  the  anterior  choroid  plexus,  the  roof  of  the  thala- 
mencephalon. 

Back  of  the  optic  lobes  and  separated  from  them  by  a  deep 
groove  is  a  narrow,  transverse  ridge,  the  cerebellum,  and  back  of 
that  is  the  medulla  oblongata,  which  is  continuous  with  the  spinal 
cord.  The  dorsal  wall  of  the  medulla  is  a  dark-colored,  vascular 
membrane  called  the  posterior  choroid  plexus,  beneath  which  is  the 
fourth  ventricle  of  the  brain.  The  triangular  depressed  area  which 
these  structures  form  is  called  the  fossa  rhomboidalis. 

The  spinal  cord  is  the  portion  of  the  central  nervous  system 
which  lies  in  the  neural  canal  of  the  spinal  column.  It  is  a 
thick,  white  band,  oval  in  cross  section,  from  which  the  paired 
spinal  nerves  spring.  At  two  points  it  is  swollen, — where  the 
spinal  nerves  which  form  the  brachial  plexus,  and  where  those 
forming  the  sciatic  plexus,  respectively,  leave  it.  The  hinder 
end  of  the  cord  tapers  rapidly  until  it  becomes  a  fine  thread 
which  extends  into  the  urostyle. 

Exercise  13.   Draw  the  dorsal  aspect  of  the  brain  and  the  spinal 
cord. 

Study  the  lateral  surface  of  the  brain  and  the  proximal  por- 
tions of  the  cranial  nerves.  Ten  pairs  of  these  nerves  are  present 
in  the  frog ;  several  pairs  are  so  small,  however,  that  they  may 
not  be  seen. 

The  first  cranial  nerve  is  the  olfactory,  which  extends  for- 
ward from  the  olfactory  lobe.  Cut  away  the  roof  of  the  ante- 
rior portion  of  the  skull  and  follow  the  two  olfactory  nerves 
forward.  Each  will  be  seen  to  branch  a  short  distance  in  front 
of  the  olfactory  lobe  and  be  distributed  to  the  walls  of  the  nasal 
capsule. 

Cut  the  olfactory  nerves.  Dissect  away  the  left  side  of  the 
skull  and  expose  the  left  surface  of  the  brain,  preserving  so  far 
as  possible  the  nerves  which  will  be  seen  coming  from  it. 

Lying  close  to  the  inner  wall  of  the  skull,  at  the  hinder 
end  of  the  orbit,  is  a  yellowish  body,  often  surrounded  by  a 
calcareous  sac.  This  is  the  Gasserian  ganglion,  and  must  not  be 


112  VEETEBEATE  ZOOLOGY 

injured.  Just  behind  the  hemispheres  the  optic  nerve,  the  second 
cranial  nerve,  issues  from  the  ventral  surface  of  the  thalamen- 
cephalon  and  extends  forward  to  the  eye.  The  thickened  side 
of  the  thalamencephalon  is  called  the  optic  thalamus. 

The  third  and  fourth  cranial  nerves  —  the  oculomotor  and  the 
trochlear  —  are  very  small  and  will  hardly  be  found ;  they  go  to 
muscles  of  the  eyeball.  The  oculomotor  springs  from  the  ven- 
tral surface  of  the  midbrain,  the  trochlear  from  the  dorsal  sur- 
face between  the  optic  lobes  and  the  cerebellum. 

The  fifth,  sixth,  seventh,  and  eighth  cranial  nerves  —  which 
are  the  trigeminal,  abducens,  facial,  and  auditory,  respectively  —  arise 
close  together  from  the  forward  end  of  the  medulla  oblongata. 
The  first  three  of  these  nerves,  together  with  the  anterior  end 
of  the  sympathetic  nerve,  are  united  in  the  Gasserian  ganglion. 
The  trigeminal  nerve  is  the  largest  of  these  three;  it  arises 
from  the  side  of  the  brain  just  beneath  the  cerebellum  and 
passes  forward  to  the  ganglion.  The  abducens  is  a  very  slen- 
der nerve  which  arises  from  the  ventral  surface  of  the  medulla 
near  the  median  line.  The  facial  and  auditory  nerves  arise  close 
together  behind  the  trigeminus.  The  latter  is  the  larger  and 
passes  directly  to  the  auditory  capsule ;  the  former  is  much 
smaller  and  passes  alongside  the  trigeminus  to  the  Gasserian 
ganglion. 

This  ganglion,  it  will  be  seen,  is  not  strictly  homologous  to 
the  same  ganglion  of  higher  vertebrates,  in  which  it  belongs 
exclusively  to  the  trigeminal  nerve.  On  this  account  it  is 
sometimes  given  another  name  in  the  frog,  and  is  called  the 
probtic  ganglion. 

Four  nerves  leave  the  Gasserian  ganglion  and  at  once  pass 
through  a  large  foramen  in  the  skull  into  the  hinder  part  of  the 
orbit.  Pull  the  eyeball  gently  forward,  cut  its  muscles  and  the 
optic  nerve,  and  remove  it.  Two  of  these  nerves — the  ophthalmic 
and  the  maxillo-mandibular  —  belong  to  the  trigeminal  and  two — 
the  palatine  and  the  hyomandibular  —  belong  to  the  facial  nerve. 
The  abducens  becomes  a  part  of  the  ophthalmic. 

The  ophthalmic  is  a  prominent  nerve  which  passes  straight  for- 
ward along  the  upper  portion  of  the  orbit  to  a  foramen  at  its 


THE  FROG  113 

forward  end,  where  it  leaves  the  orbit ;  it  then  passes  into  the 
nasal  capsule  and  divides  into  two  branches.  Near  its  base  this 
nerve  gives  off  two  small  branches  which  represent  the  abdu- 
cens  nerve  and  go  to  the  muscles  of  the  eyeball.  The  maxillo- 
mandibular  passes  laterally  from  the  ganglion  and  almost  immedi- 
ately divides  into  two  nerves,  —  the  maxillary  and  the  mandib- 
ular,  the  former  of  which  passes  along  the  mediocentral  wall  of 
the  orbit  to  the  upper  jaw,  the  latter  along  the  latero-dorsal  wall 
of  the  orbit  to  the  lower  jaw. 

The  palatine  is  the  hindermost  of  the  nerves  leaving  the  Gas- 
serian  ganglion.  It  runs  along  the  ventral  wall  of  the  orbit  and 
innervates  the  mucous  membrane  of  the  mouth,  with  which 
it  lies  in  contact.  The  hyomandibular  runs  laterally  from  the 
ganglion  to  the  angle  of  the  mouth. 

The  ninth  and  tenth  cranial  nerves — the  glossopharyngeal  and 
the  vagus  or  pneumogastric,  respectively — arise  from  the  side  of 
the  medulla,  back  of  the  auditory  nerve,  by  four  roots.  These 
uniting  form  a  single  nerve,  which  emerges  from  the  cranial 
cavity  by  a  foramen  at  the  side  of  the  foramen  magnum.  Imme- 
diately back  of  this  foramen  it  expands  into  the  large  jugal 
ganglion,  from  which  the  glossopharyngeal  and  the  vagus  proceed. 
The  former  passes  forward  to  the  tongue ;  the  latter  passes  back- 
ward along  the  pharyngeal  wall,  giving  off  branches  which 
supply  the  muscles  of  the  shoulder,  the  larynx,  heart,  lungs, 
and  stomach. 

Exercise  14.  Draw  the  lateral  aspect  of  the  brain  on  a  scale  of  3, 
and  the  cranial  nerves  so  far  as  observed. 

Study  the  ventral  surface  of  the  brain.  Cut  the  cranial  nerves 
and  remove  the  brain  from  the  skull.  Put  it  in  a  dish  of  water 
and  study  its  ventral  surface.  Identify  the  olfactory  lobe,  the 
hemispheres,  and  the  structures  belonging  to  the  thalamenceph- 
alon.  The  optic  nerves  will  be  seen  issuing  from  the  optic 
chiasma,  —  a  structure  formed  by  the  crossing  of  the  optic  nerves 
on  the  ventral  side  of  the  brain.  Behind  the  optic  chiasma  is 
the  infundibulum,  a  large  median  projection  which  is  divided  into 
a  right  and  a  left  lobe,  and  extending  from  the  hinder  end  of 


114  VEETEBEATE  ZOOLOGY 

which  is  a  flattened  body  called  the  pituitary  body,  or  hypophysis. 
This  body  is  lodged  in  a  depression  in  the  floor  of  the  cranial 
cavity,  and  usually  remains  there  after  the  brain  is  removed 
from  the  skull. 

The  ventral  portion  of  the  midbrain  is  formed  by  the  crura 
cerebri,  which  lie  beneath  the  optic  lobes  and  are  partly  concealed 
by  the  infundibulum.  Arising  from  the  crura  near  the  middle 
line  may  be  seen  the  very  delicate  oculomotor  nerves. 

The  medulla  oblongata  is  but  slightly  wider  than  the  spinal 
cord.    A  longitudinal  groove  is  present  in  the  midventral  line 
of  both. 
Exercise  15.  Draw  the  ventral  aspect  of  the  brain  on  a  scale  of  3. 

The  ventricles  of  the  brain.  With  a  sharp  scalpel  remove  the 
dorsal  wall  of  the  brain  and  expose  the  cavities  within.  Each 
hemisphere  has  a  large  cavity ;  these  are  called  the  first  and  sec- 
ond or  lateral  ventricles.  A  median  canal  called  the  foramen  of 
Munro  joins  them  with  each  other  and  with  the  third  ventricle 
which  is  a  narrow  median  space  situated  in  the  thalamencepha- 
lon.  Extending  back  from  the  third  ventricle  through  the  mid- 
brain  is  a  median  canal  called  the  aqueductus  Sylvii;  the  large 
cavity  in  each  optic  lobe  is  joined  with  it.  The  fourth  ventricle 
is  in  the  medulla;  it  is  a  triangular  space  which  at  its  hinder 
end  is  continuous  with  the  central  canal  of  the  spinal  cord. 

Exercise  16.  Draw  a  diagram  showing  these  structures. 

The  vascular  system.  This  system  is  made  up  of  the  follow- 
ing parts :  (1)  the  heart,  a  muscular  pump  which  is  continually 
driving  the  blood  to  all  parts  of  the  body ;  (2)  the  arteries,  the 
vessels  through  which  the  blood  is  carried  away  from  the  heart ; 
(3)  the  veins,  the  vessels  through  which  the  blood  is  returned  to 
the  heart;  (4)  the  capillaries,  the  minute  vessels  which  connect 
the  veins  and  arteries. 

Kill  a  frog  and  pin  it  down  as  directed  on  page  96.  Make  a 
midventral  incision  through  the  skin  from  the  tip  of  the  snout 
to  the  anus.  Note  the  prominent  cutaneous  veins  on  the  inner 
surface  of  the  skin.  Identify  first  the  abdominal  vein  through  the 


THE  FROG  115 

Ventral  wall  of  the  abdomen.  This  vein  lies  in  the  body  cavity 
against  the  ventral  abdominal  wall  and  will  appear  as  a  dark 
median  line.  Open  the  body  cavity  by  a  longitudinal  incision 
to  one  side  of  the  midventral  line,  in  order  to  avoid  cutting 
the  abdominal  vein,  from  the  anus  to  the  tip  of  the  lower  jaw. 
Take  great  care  not  to  cut  the  blood  vessels  or  other  organs 
within. 

Dissect  the  abdominal  vein  free  from  the  body  wall,  or  —  if 
this  is  difficult  on  account  of  the  small  size  of  the  frog  —  slit  the 
body  wall  on  each  side  of  the  vein,  leaving  it  attached  to  a  nar- 
row strip.  Free  the  attachments  of  the  liver  to  the  body  wall, 
spread  the  two  flaps  to  the  right  and  left,  making  a  short  trans- 
verse cut  in  each,  and  pin  them  fast,  exposing  fully  the  heart, 
liver,  and  other  internal  organs.  If  the  animal  be  a  female  the 
ovaries  should  be  removed  if  they  obscure  the  other  organs. 

The  heart  and  the  blood  vessels  leaving  and  entering  it  have 
already  been  studied  (page  101). 

The  veins.1  The  veins  may  be  divided  into  two  groups,  which 
are  (1)  the  systemic  veins,  those  which  enter  the  sinus  veno- 
sus,  with  their  branches,  bringing,  for  the  most  part,  venous 
blood  from  the  various  organs  and  tissues;  and  (2)  the  pulmonary 
veins,  which  enter  the  left  auricle,  bringing  arterial  blood  from 
the  lungs. 

We  shall  first  study  the  systemic  veins.  These  may  be  sub- 
divided into  two  groups :  (a)  the  caval  veins,  which  bring  blood 
directly  to  the  heart ;  and  (b)  the  portal  veins,  which  bring  blood 
directly  to  the  liver  and  kidneys,  whence  it  goes  to  the  heart. 

Three  large  caval  veins  are  present,  which  enter  the  sinus 
venosus;  two  of  these — the  right  and  left  precavals  —  bring  blood 
from  the  anterior  half  of  the  body,  including  the  fore  legs ;  the 
other — the  postcaval — brings  blood  from  the  posterior  half  of  the 

1  The  veins  are  usually  easily  studied  without  being  injected,  as  they  are  col- 
ored by  the  blood  in  them.  The  animals  should  not  be  dissected  fresh,  but  the 
blood  should  be  permitted  to  harden  in  the  veins  first.  If  it  is  wished  to  inject 
them,  this  should  be  done  through  the  abdominal  vein  in  both  directions  for  the 
portal  systems,  and  through  the  postcaval  vein  for  the  remaining  systemic 
veins.  The  arteries  can  be  much  better  studied  if  they  are  injected;  this  should 
be  done  through  the  ventricle  and  truncus  arteriosus. 


116  VERTEBRATE  ZOOLOGY 

body.  The  blood  brought  by  the  postcaval  veins  is  venous  blood, 
but  with  that  brought  by  the  precavals  a  certain  quantity  of 
arterial  blood  has  mingled.  The  prominent  cutaneous  veins 
which  we  have  already  observed  on  the  inner  surface  of  the  skin 
belong  to  the  precaval  system,  and  as  the  blood  in  them  has  been 
purified  by  contact  with  the  air  through  the  skin  and  the  mucous 
membrane  of  the  mouth  and  pharynx,  that  poured  by  the  pre- 
cavals into  the  heart  is  a  mixed  blood. 

Turn  the  apex  of  the  heart  forward  and  observe  the  two 
large  precaval  veins  which  enter  the  sinus  venosus  at  its  forward 
end.  Each  precaval  is  formed  by  the  union  of  three  veins, 
which  meet  immediately  in  front  of  the  heart.  These  are  the 
external  jugular,  the  most  anterior  of  the  three,  which  brings  blood 
from  the  head ;  the  innominate  vein,  the  middle  one,  which  brings 
blood  from  the  brain,  the  shoulder,  and  the  forearm;  and  the 
subclavian  vein,  the  largest  and  hindermost,  which  brings  blood 
from  the  arm  and  the  skin. 

Without  cutting  any  more  than  is  absolutely  necessary,  trace 
the  external  jugular  forward.  Near  the  hinder  margin  of  the 
head  it  is  formed  by  the  union  of  two  veins,  —  the  lingual  and 
the  internal  mandibular  veins ;  the  former  arises  in  the  tongue  ;  the 
latter  lies  along  the  inner  margin  of  the  lower  jaw. 

The  innominate  vein  is  formed  by  the  union  of  two  veins,  —  the 
internal  jugular,  which  brings  blood  from  the  head,  and  the  sub- 
scapular,  which  is  one  of  the  two  veins  returning  blood  from  the 
fore  leg. 

Several  small  glandular  bodies  are  present  near  the  external 
and  internal  jugular  veins,  of  which  the  pseudothyroid,  the  thyroid, 
and  the  thymus  glands  are  the  most  important.  The  first  of 
these,  which  is  often  wrongly  called  the  thyroid,  is  a  small 
ovoid  body  which  lies  next  to  the  inner  ventral  surface  of  the 
external  jugular.  It  arises  during  the  metamorphosis  of  the 
animal  as  a  thickening  on  the  walls  of  the  branchial  clefts. 
The  thyroid  gland  is  a  somewhat  larger  body  near  the  pseudo- 
thyroid  but  dorsal  to  it.  The  thymus  is  a  small  ovoid  body  just 
back  of  the  hinder  margin  of  the  tympanic  membrane  near  the 
internal  jugular  vein. 


THE  FKOG  ,     117 

The  subclavian  vein  is  formed  by  the  union  of  two  veins,  the 
brachial  vein,  which  is  one  of  the  two  veins  returning  blood  from 
the  fore  leg,  and  the  great  cutaneous  vein,  which  returns  it  from 
the  skin.  Follow  the  former  vein  and  its  branches.  The  latter 
vein  occupies  a  peculiar  position  in  that  it  is  partly  respiratory 
in  function.  It  lies  on  the  inner  surface  of  the  skin,  receiving 
numerous  branches,  and  may  be  traced  forward  into  the  head, 
where  it  receives  branches  from  the  mucous  membrane  of  the 
mouth  and  the  pharynx.  It  is,  however,  not  wholly  respiratory, 
as  it  also  receives  branches  from  muscles. 

Exercise  17.  Draw  a  diagrammatic  sketch  showing  the  precaval 
veins  and  their  branches  so  far  as  observed. 

The  postcaval  is  a  large  median  vein  which  enters  the  pos- 
terior end  of  the  sinus  venosus.  It  arises  between  the  kidneys 
and  runs  along  the  middorsal  wall  of  the  abdominal  cavity, 
just  beneath  the  dorsal  aorta,  to  the  liver,  through  which  it 
goes  to  the  heart.  Press  the  intestine  to  one  side,  but  without 
cutting  anything,  and  observe  it  and  its  branches. 

The  postcaval  vein  receives  the  following  branches:  the 
renal  veins,  five  or  six  pairs  in  number,  from  the  kidneys;  the 
spermatic  veins  (in  the  male)  or  ovarian  veins  (in  the  female),  from 
two  to  four  pairs  in  number,  which  join  the  postcaval  between 
the  renal  veins,  bringing  blood  from  the  genital  organs;  the 
adipose  veins,  a  pair  of  veins  from  the  fat  bodies ;  the  hepatic 
veins,  three  in  number,  from  the  liver. 

Exercise  18.  Draw  a  diagrammatic  sketch  showing  the  postcaval 
vein  and  its  branches  so  far  as  observed. 

The  portal  system  of  veins.  A  portal  vein  is  one  which  does 
not  go  directly  to  the  heart  but  either  to  the  liver  or  the  kid- 
neys, where  it  divides  up  into  capillaries  and  distributes  the 
venous  blood  throughout  these  organs.  In  the  frog  two  portal 
systems  are  present,  —  the  hepatic  portal,  by  which  blood  is  taken 
to  the  liver,  and  the  renal  portal,  by  which  it  is  taken  to  the 
kidneys. 


118  VERTEBRATE  ZOOLOGY 

The  hepatic  portal  system.  This  system  is  made  up  of  two 
large  veins  and  their  branches, —  the  abdominal  vein,  which  brings 
blood  from  the  hind  legs,  and  the  hepatic  portal  vein,  which 
brings  it  from  the  digestive  tract  and  the  spleen. 

The  abdominal  vein  is  a  median  ventral  vein  which  has  already 
been  seen.  It  is  formed  by  the  union  of  the  right  and  left  pelvic 
veins,  which  come  from  the  hind  legs.  Trace  the  abdominal  vein 
back  and  find  them.  Note  the  branches  the  abdominal  vein 
receives  from  the  gall  bladder,  the  heart,  the  urinary  bladder, 
and  those  from  the  body  wall.  Cut  the  abdominal  vein  in  the 
middle ;  turn  the  liver  forward  and  expose  its  dorsal  surface ; 
fasten  it  with  pins  'in  this  position. 

Trace  the  abdominal  vein  forward  to  the  liver.  Just  to  the 
left  of  the  gall  bladder  it  divides  into  three  branches,  two  of 
which  go  to  the  right  and  left  lobes  of  the  liver,  while  the  third 
joins  the  hepatic  portal  vein. 

Study  the  hepatic  portal  and  its  branches.  It  is  a  short,  wide 
vein  which  lies  in  the  mesentery  and  enters  the  left  lobe  of  the 
liver.  Near  the  point  where  it  enters  the  liver  it  is  joined  by 
the  branch  of  the  abdominal  vein  just  mentioned.  The  hepatic 
portal  receives  numerous  branches,  called  the  intestinal  veins, 
which  lie  in  the  mesentery  and  come  to  it  from  the  small  and 
large  intestines.  It  also  receives  the  splenic  vein  from  the  spleen, 
the  two  large  gastric  veins  from  the  stomach,  a  gastroduodenal  vein 
from  the  stomach  and  duodenum,  and  a  number  of  small  pan- 
creatic veins  from  the  pancreas.  The  anterior  portion  of  its  course 
is  through  the  pancreas. 

Exercise  19.  Draw  a  semidiagrarnmatic  sketch  showing  the 
hepatic  portal  system;  also  outlines  of  the  organs  with 
which  it  enters  into  relations. 

The  renal  portal  system.  This  system  is  made  up  of  veins 
from  the  hind  legs,  the  dorsal  body  wall,  the  kidneys,  and,  in 
the  female,  the  oviducts ;  it  is  joined  with  the  abdominal  vein 
by  the  pelvic  veins,  which  have  just  been  observed,  and  with 
the  kidneys  by  the  renal  portal  veins. 


THE  FROG  119 

Two  veins  —  the  femoral  and  the  sciatic  —  collect  the  blood  of 
the  hind  leg  on  each  side  of  the  body.  The  femoral  is  the  larger 
of  these.  It  is  a  large  vein  which  appears  on  the  ventral  surface 
of  the  leg>  where  it  divides  into  two  branches.  The  larger  of 
these  is  the  pelvic  vein,  just  mentioned,  the  other  is  the  external  iliac. 

The  sciatic  vein  lies  on  the  back  of  the  thigh.  It  passes 
forward  and  joins  the  external  iliac.  The  vein  so  formed  is 
the  renal  portal,  which  runs  forward  to  the  outer  margin  of 
the  kidney  at  its  hinder  end.  The  vein  then  continues  within 
the  kidney  close  to  its  lateral  margin,  and  gives  off  numerous 
branches,  which  break  up  into  capillaries  in  the  kidney.  At 
about  the  middle  of  the  kidney  a  vein  comes  from  the  side  and 
joins  the  renal  portal.  This  is  the  dorsolumbar  vein ;  it  collects 
blood  from  the  dorsal  body  wall.  In  the  female  a  large  number 
of  veins  from  the  oviduct  also  enter  the  lateral  margin  of  the 
kidney  and  join  the  renal  portal  vein. 

Trace  the  abdominal  vein  back  and  find  the  pelvic  veins. 
Follow  one  of  the  pelvic  veins  back  to  the  base  of  the  leg, 
where  it  will  be  seen  to  be  one  of  the  two  branches  into  which 
the  prominent  femoral  vein  divides.  Trace  the  other  branch, 
the  external  iliac,  forward  to  its  point  of  union  with  the  sciatic 
vein ;  trace  the  renal  portal  vein  to  the  kidney.  Study  the  dis- 
tribution of  the  femoral  and  sciatic  veins  in  the  leg.  Observe 
the  dorsolumbar  vein  entering  the  kidney  in  the  middle  of  its 
lateral  margin  and  study  its  distribution.  Observe  the  oviducal 
veins,  if  the  animal  be  a  female. 

Exercise  20.  Draw  a  semidiagrammatic  sketch  showing  the  renal 
portal  system,  together  with  an  outline  of  the  organs  with 
which  the  veins  enter  into  relations. 

The  pulmonary  veins.  The  common  pulmonary  enters  the  left 
auricle.  It  is  a  very  short  vein  and  is  formed  by  the  union  of  the 
right  and  left  pulmonaries,  which  come  from  the  right  and  left  lungs 
respectively.  Each  pulmonary  vein  lies  along  the  medial  side  of 
the  lung,  the  right  pulmonary  being  somewhat  longer  than  the 
left.  Turn  the  apex  of  the  heart  forward  and  find  these  veins. 

Exercise  21.  Draw  a  diagram  of  the  entire  venous  system. 


120  VEETEBEATE   ZOOLOGY 

The  arteries.1  All  the  blood  in  the  heart  leaves  it  through 
the  truncus  arteriosus,  the  structure  of  which  has  already  been 
observed.  At  its  anterior  end  the  truncus  divides  into  a  right 
and  a  left  branch,  each  of  which  after  passing  through  the  peri- 
cardium again  divides  into  three  branches,  —  the  carotid,  systemic, 
and  pulmocutaneous  aortic  arches.  The  last  named  of  these  arches, 
which  is  the  hindermost  in  position,  branches  off  from  the  others  a 
short  distance  in  front  of  the  pericardium;  the  other  two  usually 
remain  together  a  short  distance  before  separating. 

The  anterior  aortic  arch  —  the  carotid  —  passes  forward  and 
dorsally  a  short  distance  and  then  divides  into  two  vessels,  — 
the  internal  and  the  external  carotid  arteries.  At  this  point  the  walls 
of  the  arteries  are  thickened  and  spongy,  and  the  ovoid  structure 
thus  formed  is  called  the  carotid  gland;  it  is  not  a  gland,  how- 
ever, but  probably  acts  as  an  accessory  heart.  The  internal 
carotid,  the  larger  of  the  two,  goes  dorsally  and  then  forward 
and  supplies  the  brain,  the  orbit,  and  the  mucous  membrane  of 
the  roof  of  the  mouth.  The  external  carotid  passes  directly  for- 
ward and  supplies  the  tongue  and  the  muscles  of  the  lower  jaw. 

The  posterior  aortic  arch  —  the  pulmocutaneous  —  takes  blood 
to  the  lungs  and  skin  to  be  oxygenated.  On  each  side  just  back 
of  the  carotid  gland  it  divides  into  two  arteries, — the  pulmonary 
and  the  great  cutaneous.  The  former  passes  back  a  short  distance 
and  then  divides  into  three  arteries  which  traverse  the  walls  of 
the  lung.  The  latter  passes  first  forward  and  dorsally  and  then 
backward  along  the  inner  surface  of  the  skin,  sending  branches 
to  the  head  and  the  muscles  of  the  body  wall. 

Exercise  22.  Draw  a  semidiagrammatic  sketch  showing  the  dis- 
tribution of  these  arteries  so  far  as  observed. 

The  middle  arch,  the  systemic,  supplies  the  greater  part  of  the 
body  with  blood.  The  two  sides  of  the  arch  pass  dorsally,  one 
on  each  side,  around  the  oesophagus  to  the  upper  side  of  the 
body  cavity,  where  they  meet  and  form  the  dorsal  aorta,  or  aorta 
descendens.  This  vessel  runs  just  beneath  the  spinal  column  to 

1  The  arterial  system  can  be  best  studied  after  it  has  been  injected ;  this 
should  be  done  through  the  ventricle  and  the  truncus  arteriosus. 


THE  FKOG  121 

the  hinder  part  of  the  body  cavity,  where  it  divides  into  two 
arteries,  —  the  iliacs,  —  which  go  to  the  legs. 

Lift  up  the  stomach  and  find  the  aorta  descendens ;  follow  it 
forward  to  the  meeting  point  of  the  two  sides  of  the  systemic 
arch,  and  then  follow  each  side  of  the  arch  to  the  heart.  Each 
side  of  the  arch  gives  off  the  subclavian,  occipito-vertebral, 
cesophageal,  and  laryngeal  arteries,  of  which  the  subclavian  is 
foremost  in  position. 

The  last  three  of  these  arteries  leave  the  arch  near  together. 
The  subclavian  is  the  largest  and  supplies  the  shoulder  and  fore 
leg.  Follow  it  and  its  branches.  The  cesophageal  and  occipito- 
vertebral  are  close  together  and  go  to  the  head,  a  branch  of  the 
latter — the  vertebral — also  passing  back  along  the  dorsal  surface 
of  the  spinal  column.  The  laryngeal  arises  in  front  of  the  others 
and  goes  to  the  head. 

Just  behind  the  point  of  union  of  the  two  sides  of  the  sys- 
temic arch  the  dorsal  aorta  gives  off  the  cceliaco-mesenteric  artery. 
Observe  that  this  large  artery  is  a  continuation  of  and  receives 
most  of  the  blood  of  the  left  systemic  arch.  The  dorsal  aorta 
thus  receives  most  of  its  blood  from  the  right  arch. 

The  coeliaco-mesenteric  artery  supplies  the  stomach  and  intes- 
tine with  blood.  It  soon  divides  into  two  branches,  —  the  cceliac 
artery  and  the  anterior  mesenteric,  the  former  supplying  the  stomach, 
liver,  and  pancreas,  the  latter  the  small  intestine,  rectum,  and 
spleen. 

Posteriorly  to  the  coeliaco-mesenteric  artery  four  to  six  pairs 
of  urogenital  arteries  spring  from  the  ventral  surface  of  the  dorsal 
aorta  and  go  to  the  genital  organs,  kidneys,  and  fat  bodies. 
Several  pairs  of  small  lumbar  arteries  also  spring  from  the  dorsal 
surface  of  the  aorta  and  supply  the  dorsal  body  wall.  Near  the 
hinder  end  of  the  dorsal  aorta  the  small  median  posterior  mesen- 
teric artery  leaves  its  ventral  surface  and  runs  to  the  rectum. 

The  common  iliac  arteries — which  are  formed  by  the  division  of 
the  dorsal  aorta, — are  large  vessels  which  supply  the  hind  legs. 
A  short  distance  from  its  origin  each  gives  off  two  small  arte- 
ries,— the  hypogastric,  which  supplies  the  rectum,  bladder,  and 
ventral  body  wall;  and  the  femoral,  which  goes  to  the  thigh. 


122  VERTEBRATE  ZOOLOGY 

After  giving  off  these  arteries  the  common  iliac  is  knowii  as 
the  sciatic  artery.     Follow  it  and  its  branches  into  the  leg. 

Exercise  23.  Draw   a  semidiagrammatic   sketch  showing  these 
arteries  so  far  as  they  have  been  observed. 

Exercise  24.  Draw  a  diagram  of  the  entire  arterial  system. 

The  muscular  system.  Most  muscles  in  the  land  vertebrates 
are  attached  at  their  two  ends  by  means  of  tendons.  One  end 
is  usually  attached  to  a  more  or  less  fixed  and  the  other  to  a 
more  movable  portion  of  the  body,  the  former  being  called  the 
origin  of  the  muscle  and  the  latter  its  insertion.  The  middle  part 
of  the  muscle  is  called  the  belly;  by  its  contraction  the  origin 
and  insertion,  and  with  them  the  skeletal  pieces  to  which  they 
are  attached,  are  brought  nearer  together.  Muscles  are  usually 
attached  to  the  bones  and  cartilages ;  thick  fibrous  membranes, 
called  aponeuroses,  which  often  cover  muscles  and  other  organs, 
may,  however,  serve  the  same  purpose. 

Kill  a  frog  and  completely  remove  the  skin  from  the  body, 
without  injuring  any  of  the  muscles.  Inasmuch  as  they  are 
more  or  less  transparent  when  fresh,  it  is  well  to  let  the  animal 
lie  in  alcohol  or  formalin  before  the  muscles  are  studied. 

Fasten  the  frog  on  its  back,  with  its  head  away  from  you,  by 
means  of  a  pin  through  the  tip  of  the  nose  and  one  through 
each  foot,  and,  without  cutting  anything,  study  the  muscles  of 
the  ventral  side  of  the  body.  On  the  head  the  broad,  thin  sub- 
mandibular  muscle  —  the  fibers  of  which  are  transverse  in  direc- 
tion—  stretches  across  from  one  side  of  the  lower  jaw  to  the 
other.  A  median  tendon  separates  the  right  half  of  it  from 
the  left  half.  A  narrow  strand  of  muscle,  the  subhyoid,  lies  at 
the  hinder  end  of  the  submandibular,  with  fibers  "parallel  to  its 
fibers  and  attached  to  it  in  the  medial  area.  The  lateral  ends 
of  the  subhyoid  find  their  origin  in  the  hyoid  cartilage. 

At  the  forward  end  of  the  trunk  is  a  group  of  four  muscles 
which  radiate  from  the  base  of  the  fore  leg  on  each  side  toward 
the  medial  area  of  the  body  and  may  be  called  the  pectoral  group. 
Beneath  the  medial  ends  of  these  muscles  between  the  fore  legs 


THE  FROG  123 

will  be  seen  the  delicate  sternum,  or  breastbone.  The  foremost 
of  these  muscles  is  the  coraco-radial.  It  is  a  wide  muscle,  the 
hinder  half  of  which  is  concealed  beneath  the  muscle  next 
behind  it.  From  its  distal  end  a  long  tendon  passes  along  the 
humerus  to  the  forearm.  The  function  of  this  muscle  is  to 
bend  the  forearm. 

The  other  three  muscles  of  this  group  are  divisions  of  the 
pectoral  muscle.  The  anterior  two  divisions,  like  the  coraco-radial, 
have  their  origin  in  the  breastbone  near  the  median  line.  The 
hindermost  division,  which  is  the  largest,  has  its  origin  in  the 
outer  edge  of  the  broad  aponeurosis,  which  occupies  the  median 
area  of  the  abdomen.  All  the  divisions  of  the  pectoral  muscle 
have  their  insertion  near  the  proximal  end  of  the  humerus  in  the 
upper  arm  and  serve  to  bend  the  arm  back. 

Lying  in  front  of  the  pectorals  is  the  deltoid  muscle.  It  consists 
of  two  principal  portions,  —  an  anterior  and  a  posterior  portion, 
—  both  of  which  arise  near  the  median  line  along  the  forward 
border  of  the  pectorals.  They  are  inserted  in  the  humerus  and 
cover  the  insertions  of  the  pectoral  muscles.  Determine  the 
action  of  the  deltoid  muscle. 

Back  of  the  breastbone  are  the  abdominal  muscles,  which  form  the 
ventral  and  lateral  walls  of  the  abdomen.  Three  pairs  are  present, 
the  rectus  abdominis,  the  external  oblique,  and  the  transversus. 

Extending  from  the  hinder  end  of  the  breastbone  to  the  hinder 
end  of  the  trunk  is  the  aponeurosis  just  mentioned,  —  a  broad 
median  band  of  connective  tissue  covering  the  midventral  area 
of  the  abdomen.  A  similar  aponeurosis  is  also  present  in  the 
middorsal  area. 

The  rectus  abdominis  muscles  are  a  pair  of  longitudinal  muscles 
which  lie  in  the  midventral  area  beneath  the  aponeurosis.  A 
narrow  tendinous  band  called  the  linea  alba  lies  in  the  median 
line  and  separates  the  right  from  the  left  rectus.  There  are 
also  present  in  these  muscles  four  or  five  tendinous  bands 
which  divide  them  into  segments.  This  segmentation,  which 
also  appears  in  the  rectus  abdominis  of  many  higher  vertebrates, 
including  man,  is  an  inheritance  from  the  metameric  condition 
of  the  body  muscles  in  the  fishes  and  the  urodelan  amphibians. 


124  VERTEBRATE  ZOOLOGY 

The  external  oblique  muscle  forms  the  lateral  wall  of  the  abdo- 
men on  each  side.  It  is  a  broad,  thin  muscle  which  extends 
from  the  middorsal  to  the  midventral  aponeurosis,  its  fibers 
having  an  oblique  direction.  Immediately  beneath  this  muscle 
is  the  transversus,  the  fibers  of  which  have  a  transverse  direction. 

Exercise  25.  Draw  the  ventral  aspect  of  the  body,  showing  these 
muscles. 

Study  the  superficial  muscles  of  the  ventral  surface  of  the 
hind  leg.  The  longest  muscle  of  the  thigh  is  the  sartorius.  It  is 
a  long  band  which  extends  along  the  middle  of  the  thigh  from 
the  pelvis  to  the  proximal  end  of  the  shank.  Just  in  front  of  it 
is  a  broad  muscle  —  the  vastus  internus  —  which  forms  the  ante- 
rior border  of  the  thigh.  It  also  forms  the  anterior  portion  of  a 
threefold  muscle,  —  the  triceps  extensor  femoris,  —  which  is  the 
principal  extensor  muscle  of  the  thigh.  The  other  two  portions 
of  this  muscle  are  on  the  upper  side  of  the  leg ;  they  are  the 
rectus  anticus  femoris  and  the  vastus  externus,  —  the  latter  being 
posterior  to  the  former. 

Posterior  to  the  sartorius  on  the  ventral  surface  are  three 
muscles,  —  the  adductor  magnus,  the  rectus  internus  major,  and  the 
rectus  internus  minor,  the  latter  of  which  forms  the  hinder  margin 
of  the  thigh.  These  are  all,  together  with  the  sartorius,  flexors 
of  the  leg. 

On  the  lower  leg  or  shank  the  large  muscle  which  forms  the 
calf  is  the  gastrocnemius.  At  its  lower  end  is  the  tendon  of  Achilles, 
which  passes  over  the  ankle  and  is  continued  in  the  plantar 
aponeurosis,  a  broad  tendinous  band  covering  the  sole  of  the  foot. 
The  front  side  of  the  shank  is  formed  by  the  tibialis  anticus 
muscle. 

Exercise  26.  Draw  the  ventral  aspect  of  the  hind  leg. 

Study  the  superficial  muscles  of  the  dorsal  surface  of  the  leg. 
The  anterior  half  of  the  surface  of  the  thigh  is  occupied  by  two 
muscles  already  noted,  —  the  rectus  anticus  femoris  and  the  vas- 
tus externus.  Posterior  to  the  last-named  muscle  are  the  biceps 


THE  FKOG  125 

femoris,  the  semimembranosus,  and  the  rectus  internus  minor,  —  the 
latter  forming  the  hinder  margin  of  the  leg. 

On  the  shank  will  be  seen  the  large  gastrocnemius,  forming  the 
calf  of  the  leg,  the  tibialis  anticus,  forming  its  anterior  border, 
and  the  peroneus  between  the  two. 

Exercise  27.  Draw  the  dorsal  aspect  of  the  leg. 

Without  injuring  the  bones  trace  each  of  these  muscles  to  its 
origin  and  insertion  and  determine  which  muscles  are  extensors 
and  which  are  flexors. 

The  skeletal  system.  This  system  is  made  up  of  two  por- 
tions, the  exoskeleton  and  the  endoskeleton.  The  exoskeleton  in  verte- 
brates consists  of  the  hardened  bony  or  horny  structures  which 
develop  in  the  skin  and  furnish  an  external  protection  to  the 
animal.  These  structures  are  very  poorly  represented  in  the 
anuran  amphibians.  The  skin  is  naked,  no  bony  or  horny  scales 
or  other  hardened  integumental  structures  being  present.  The 
toes  are  also  without  claws.  The  only  exoskeletal  structures 
are  the  teeth  and  certain  bones  called  membrane  bones  which 
form  a  part  of  the  skull.  These  bones  are,  however,  so  inti- 
mately joined  with  the  other  bones  and  cartilages  of  the  skull 
that  they  will  be  studied  in  connection  with  them. 

The  endoskeleton  consists  of  the  bony  and  cartilaginous  frame- 
work of  the  body.  It  may  be  divided  into  the  axial  skeleton, 
which  includes  the  skull  and  the  spinal  column,  and  the  appen- 
dicular  skeleton,  which  includes  the  framework  of  the  two  pairs  of 
appendages,  i.e.  the  legs  and  the  girdles  which  join  them  with 
the  trunk.  The  breastbone  may  also  be  conveniently  studied 
with  the  appendicular  skeleton. 

The  appendicular  skeleton.  The  anterior  appendages  consist 
of  the  fore  legs  and  the  pectoral  girdle.  This  girdle  is  formed  of  a 
right  and  a  left  half  which  meet  midventrally ;  here  they  enter 
into  a  close  union  with  the  breastbone  and  form  with  it  a  bony 
and  cartilaginous  ring  which  almost  completely  encircles  the 
forward  part  of  the  trunk. 

Each  half  of  the  pectoral  girdle  supports  one  of  the  fore  legs 
and  is  composed  of  two  portions,  —  a  dorsal  and  a  ventral  portion. 


126  VERTEBRATE   ZOOLOGY 

The  former  portion  consists  of  two  skeletal  pieces  of  nearly 
equal  size, — the  suprascapula  and  the  scapula,  —  which  lie  respec- 
tively on  the  dorsal  and  lateral  sides  of  the  body.  The  supra- 
scapula —  the  dorsal  half  —  is  a  broad,  thin  plate  which  extends 
upward  over  the  spinal  column.  Its  broad,  free  dorsal  end  is 
composed  of  cartilage ;  the  remainder  of  it  is  bone.  The  scapula 
is  an  elongated  plate  of  bone  which  extends  from  the  supra- 
scapula to  the  ventral  side  of  the  body. 

The  ventral  portion  of  the  pectoral  girdle  consists  of  two 
bony  and  three  cartilaginous  skeletal  pieces.  The  two  bones 
are  the  coracoid  and  the  clavicle,  the  former  being  the  larger  and 
the  more  posterior  in  position,  and  extending  from  the  scapula 
to  the  midventral  line.  Joining  them  and  the  scapula  is  an 
irregular  cartilaginous  mass  called  the  paraglenoid  cartilage,  in  the 
hinder  side  of  which  is  a  depression,  the  glenoid  cavity,  in  which 
the  humerus  articulates.  Lying  along  the  entire  hinder  surface 
of  the  clavicle  is  a  slender  strip  of  cartilage,  the  procoracoid,  and 
at  the  medial  end  of  the  coracoid  and  clavicle  is  another  narrow 
strip,  the  epicoracoid  cartilage,  which  joins  the  like  cartilage  of  the 
opposite  side  in  the  median  line. 

The  breastbone,  or  sternum,  lies  in  the  medial  area  and  consists  of 
two  portions,  —  the  sternum  and  the  episternum,  —  each  of  which 
is  made  up  of  a  bone  and  a  cartilage.  The  sternum  lies  immedi- 
ately back  of  the  coracoids.  The  bony  half  is  in  front  of  the  car- 
tilaginous portion,  which  is  a  broad,  thin,  bilobed  plate.  The 
episternum  lies  in  front  of  the  clavicles.  The  bony  half  is  behind 
the  cartilaginous  portion,  which  is  a  thin,  round  plate. 

Remove  the  pectoral  girdle  with  the  fore  leg  from  the  body. 
Inasmuch  as  it  is  not  joined  with  the  vertebral  column  it  may 
be  removed  by  freeing  it  from  the  muscles  in  which  it  is 
imbedded.  First  locate  accurately  the  delicate  cartilaginous 
portions  of  the  sternum  and  the  episternum;  carefully  locate 
also  the  delicate  suprascapula  on  each  side  of  the  body.  Insert 
then  the  blade  of  a  small  scalpel  under  the  suprascapula  on  one 
side  and  free  it  from  the  muscles  which  lie  over  it.  Pass  the 
scalpel  down  to  the  scapula  and  then  to  the  ventral  portion  of 
the  pectoral  girdle.  Do  the  same  on  the  opposite  side  of  the  body, 


THE  FROG  127 

and  finally  remove  the  entire  girdle  with  the  breastbone  from 
the  body.  Disarticulate  and  remove  the  two  fore  legs  and  very 
carefully  clean  away  the  muscles. 

Exercise  28.  Draw  an  outline  sketch  of  the  pectoral  girdle  and 
breastbone,  representing  them  in  one  plane ;  carefully  label 
all  their  parts. 

The  fore  leg.  The  skeleton  of  the  fore  leg  is  composed  of 
three  divisions,  —  a  proximal,  a  middle,  and  a  distal  division. 

The  proximal  division,  or  upper  arm,  is  composed  of  a  single 
bone,  the  humerus.  The  head  of  it,  which  is  cartilaginous,  fits  in 
the  glenoid  cavity  and  forms  the  shoulder  joint.  Just  below  it 
on  the  ventral  side  is  a  prominent  ridge  called  the  crista  ventralis, 
in  which  the  pectoral  muscles  are  inserted.  At  the  distal  end 
is  a  large  round  projection,  on  each  side  of  which  is  a  ridge 
forming  the  articular  surface  for  the  bone  of  the  next  division. 

The  middle  division,  or  forearm,  is  composed  of  a  single  bone, 
the  radio-ulna.  It  is  formed  by  the  fusion  of  the  radius  and  ulna, 
the  two  bones  which  are  present  in  the  forearm  of  most  verte- 
brates. The  larger  part  of  this  bone  is  the  radius.  Its  proximal 
end  is  concave,  the  projecting  process  on  it  being  the  olecranon, 
or  elbow.  Its  distal  end  has  two  articular  surfaces. 

The  distal  division  is  composed  of  the  carpus  or  wrist  and  the 
hand.  The  carpal  bones  are  six  in  number,  arranged  in  two 
rows,  a  proximal  and  a  distal  row.  The  hand  is  made  up  of  five 
digits,  of  which  the  first  digit,  or  thumb,  is  very  small  and  rudi- 
mentary. Each  of  the  other  four  digits  is  composed  of  two 
parts,  —  the  metacarpus,  the  long  proximal  bone  which  articulates 
with  the  carpus;  and  the  phalanges,  two  or  three  small  bones 
which  form  the  finger.  The  thumb  contains  a  metacarpus  alone. 

Exercise  29.  Draw  the  fore  leg  in  outline,  showing  accurately  all 
the  bones  and  cartilages ;  label  them  all  carefully. 

The  posterior  appendages.  These  consist  of  the  hind  legs,  and 
the  pelvic  girdle  which  joins  them  with  the  trunk. 

The  pelvic  girdle,  like  the  pectoral,  is  composed  of  a  right  and 
a  left  half  which  meet  ventrally  and  form  an  arch.  The  dorsal 


128  VEETEBEATE  ZOOLOGY 

ends  of  the  arch  articulate  with  the  last  vertebra  of  the  spinal 
column,  while  at  its  ventral  end,  on  each  side,  is  the  acetabulum, 
the  articular  surface  of  the  hind  leg.  Extending  backward 
from  the  last  vertebra  between  the  two  sides  of  the  pelvic  girdle 
is  the  long  bone  called  the  urostyle,  which  forms  the  hinder  part 
of  the  spinal  column. 

Each  half  of  the  pelvic  girdle  is  composed  of  two  portions,  a 
dorsal  and  lateral  portion  and  a  ventral  portion.  The  former  consists 
of  the  long,  slightly  arched  ilium,  which  forms  the  side  of  the 
arch  and  articulates  dorsally  with  the  last  vertebra.  The  ven- 
tral portion  is  disk-shaped  and  is  composed  of  the  ventral  end 
of  the  ilium,  a  small  triangular  bone  called  the  ischium,  and  a 
small  triangular  cartilage  called  the  pubis ;  the  pubis  is  anterior 
to  the  ischium  in  position.  The  ilium,  ischium,  and  pubis  cor- 
respond to  the  scapula,  coracoid,  and  procoracoid,  respectively, 
in  the  pectoral  girdle. 

Carefully  strip  the  muscles  from  the  pelvic  girdle,  disarticu- 
late it  from  the  vertebral  column,  and  remove  it  and  the  hind 
legs  from  the  body.  Disarticulate  the  legs  and  thoroughly 
clean  the  pelvis. 

Exercise  30.  Draw  two  views  of  the  pelvis  on  a  scale  of  2,  one 
of  the  lateral  aspect  and  one  of  the  dorsal  aspect. 

The  hind  leg.  The  skeleton  of  this  leg  closely  corresponds 
to  that  of  the  fore  leg.  It  is  made  up  of  three  divisions, — 
a  proximal,  a  middle,  and  a  distal  division. 

The  proximal  division,  or  thigh,  is  composed  of  a  single  bone, 
the  femur,  the  head  of  which  fits  into  the  acetabulum  and  forms 
the  hip  joint. 

The  middle  division,  or  shank,  is  composed  of  a  single  bone,  the 
tibio-fibula.  It  is  formed  by  the  fusion  of  the  tibia  and  the  fibula, 
the  two  bones  which  are  present  in  the  shank  of  most  verte- 
brates. The  line  of  division  between  the  two  is  very  distinct. 

The  distal  division  is  composed  of  the  tarsus  or  ankle  and  the 
foot.  The  tarsal  bones  are  five  in  number,  arranged  in  two  rows, 
—  a  proximal  and  a  distal  row.  The  proximal  row  consists  of 
two  long  bones,  —  the  astragalus  and  the  calcaneum,  —  which  are 


THE  FKOG  129 

united  at  both  ends.  The  latter  is  on  the  inner  side  of  the  foot 
and  corresponds  to  the  heel  bone.  The  distal  row  is  composed 
of  three  very  small  bones.  The  foot  is  made  up  of  six  digits, 
of  which  one  is  supernumerary  and  rudimentary;  the  others 
are  the  five  digits  which  characterize  the  typical  vertebrate 
foot.  The  supernumerary  digit  is  on  the  inner  side  of  the 
foot  and  consists  of  from  one  to  three  small  bones.  Each  of 
the  other  five  is  composed  of  two  parts,  —  the  metatarsus,  a  long 
bone  which  articulates  with  the  tarsus ;  and  the  phalanges,  two  to 
four  smaller  bones  which  form  the  toe.  The  first  digit  on  the 
inner  side  of  the  foot  corresponds  to  the  big  toe. 

Exercise  31.  Draw  the  ventral  aspect  of  the  leg  on  a  scale  of  2, 
showing  accurately  the  outlines  of  the  bones  and  cartilages. 

The  axial  skeleton ;  the  vertebral  column.  Strip  the  muscles 
from  the  back.  Disarticulate  the  head  from  the  trunk. 

The  vertebral  column  is  composed  of  nine  vertebrae  and  a 
long  unsegmented  bone  called  the  urostyle,  which  forms  its  pos- 
terior portion.  Four  regions  may  be  distinguished  in  it,  —  a  cervi- 
cal region,  consisting  of  the  first  vertebra ;  a  thoraco-lumbar  region, 
consisting  of  the  succeeding  seven,  vertebrae  ;  a  sacral  region,  con- 
sisting of  the  last  vertebra ;  and  the  urostyle,  which  represents  a 
caudal  region. 

A  vertebra  is  made  up  of  the  following  parts :  the  centrum,  or 
body,  which  is  the  cylindrical  ventral  portion;  the  neural  arch, 
on  the  dorsal  side  of  the  centrum,  which  with  it  forms  the  neural 
canal ;  and  the  transverse  processes,  a  pair  of  long  lateral  projec- 
tions. The  neural  arch  is  made  up  of  a  pair  of  neural  processes, 
which  form  its  sides,  and  the  median  neural  spine,  or  spinous 
process,  which  forms  its  roof.  On  the  anterior  surface  of  the 
neural  arch  is  a  pair  of  articular  projections  called  the  prezyga- 
pophyses ;  on  the  posterior  surface  is  a  pair  of  corresponding 
postzygapophyses.  It  is  by  these  projections  that  the  vertebrae 
are  locked  together.  Note  the  difference  in  size  in  the  trans- 
verse processes  of  the  various  vertebrae. 

The  first  or  cervical  vertebra  is  called  the  atlas.  It  differs 
from  the  other  vertebrae  principally  in  that  it  has  no  transverse 


130  VERTEBRATE  ZOOLOGY 

processes  (although  occasionally  they  have  been  found),  no 
prezygapophyses,  and  a  thinner  centrum.  On  its  anterior  sur- 
face is  a  pair  of  depressions  into  which  fit  the  articular  pro- 
cesses of  the  skull, — the  condyles.  The  last  vertebra,  or  sacrum, 
has  large  transverse  processes  with  which  the  pelvic  girdle 
articulates.  It  lacks  postzygapophyses,  and  on  the  hinder  sur- 
face of  the  centrum  is  a  pair  of  prominences  which  articulate 
with  the  urostyle. 

Between  each  two  vertebrae  on  each  side  and  between  the 
ninth  vertebra  and  the  urostyle  is  an  interval  called  the  inter- 
vertebral  foramen,  through  which  a  spinal  nerve  passes.  In  the 
urostyle  on  each  side  near  the  forward  end  is  the  foramen  of 
the  posterior  spinal  nerve. 

Exercise  32.  Draw  a  view  of  the  ventral  aspect  of  the  vertebral 
column. 

Exercise  33.  Remove  the  second  vertebra,  clean  it  thoroughly, 
and  draw  a  view  of  its  hinder  end. 

The  skull  is  composed  of  two  regions,  —  the  cranium  and  the 
visceral  skeleton.  The  former  incloses  and  protects  the  brain  and 
the  organs  of  special  sense ;  the  latter  surrounds  the  mouth  and 
pharynx,  forming  the  framework  of  the  jaws  and  tongue. 

Both  of  these  regions  are  composed  exclusively  of  cartilage 
at  an  early  period  of  the  life  of  the  animal,  and  certain  portions 
of  them  remain  cartilaginous.  As  the  young  animal  develops, 
however,  certain  parts  of  the  cartilage  are  replaced  by  bone. 
Besides  these  cartilage  bones,  as  they  are  called,  other  bones  also 
make  their  appearance  which  develop  not  in  cartilage  but  in 
the  skin  and  in  connective-tissue  membranes  which  cover  the 
skull;  these  are  called  membrane  bones.  Thus,  so  far  as  the  mate- 
rial of  which  it  is  made  up  is  concerned,  the  skull  is  composed 
of  cartilage,  cartilage  bones,  and  membrane  bones. 

We  shall  begin  with  the  study  of  the  lower  jaw  and  the 
hyoid  apparatus  which  supports  the  tongue.  These  structures 
belong  to  the  visceral  skeleton.  The  hyoid  is  a  thin  plate  of 
cartilage,  with  a  pair  of  long  anterior  and  a  pair  of  short 


THE  FROG  131 

posterior  projections,  which  is  imbedded  in  the  muscles  of  the 
lower  jaw.  The  thin  plate  is  called  the  body  of  the  hyoid. 
The  anterior  projections  —  or  anterior  cornua — are  slender,  cylin- 
drical cartilages  which  extend  first  backward  to  the  hinder 
end  of  the  lower  jaw,  and  then  upward  to  the  base  of  the 
cranium;  the  posterior  cornua  are  a  pair  of  straight,  bony  rods 
which  extend  back  from  the  hinder  end  of  the  body  of  the 
hyoid. 

The  lower  jaw,  or  mandible,  is  a  paired  structure  which  is  com- 
posed on  each  side  of  two  bones  called  the  angular  and  the 
dentary,  and  a  cartilage.  The  latter  is  called  Meckel's  cartilage: 
it  forms  the  primitive  mandible  at  the  time  in  the  development 
of  the  animal  when  the  entire  skull  is  cartilaginous,  and  persists 
as  the  axis  of  the  adult  mandible.  Its  hinder  end  is  widened 
and  articulates  with  the  upper  jaw. 

The  greater  part  of  Meckel's  cartilage,  however,  is  not  free, 
but  isensheathed  by  two  long  membrane  bones,  —  the  angular  and 
the  dentary,  just  mentioned.  The  former  of  these  bones  covers  the 
ventral  and  medial  sides  of  the  cartilage  along  almost  its  entire 
extent ;  on  the  outer  side  the  hinder  part  of  the  cartilage  is  still 
exposed.  The  dentary  bone  consists  of  two  portions,  —  a  long, 
flat  lateral,  and  a  small  medial  portion.  The  former  covers  the 
outer  side  of  most  of  the  forward  half  of  Meckel's  cartilage; 
the  latter  is  much  smaller  and  lies  at  the  forward  end  of  the 
cartilage.  The  mandible  is  without  teeth. 

Without  disarticulating  the  lower  jaw,  carefully  dissect  the 
hyoid  apparatus  from  the  floor  of  the  mouth. 

Exercise  34.  Draw  the  hyoid  apparatus  on  a  large  scale. 

Exercise  35.  Remove  and   clean    the    mandible   and   draw  the 
dorsal  aspect. 

Thoroughly  clean  the  remainder  of  the  skull  but  do  not  remove 
the  tympanum ;  the  process  is  expedited  by  boiling  it  a  short 
time. 

Observe  the  great  flatness  and  breadth  of  the  skull.  At  its 
hinder  end  is  the  foramen  magnum,  the  large  opening  through 


132  VEKTEBEATE  ZOOLOGY 

which  the  spinal  cord  enters  the  brain  cavity.  The  cranium, 
which  protects  the  brain  and  the  special  sense  organs,  is  the 
narrow  medial  portion  of  the  skull.  On  each  side  of  it  is  the 
large  oval  opening  in  which  the  eye  lies.  The  arch-shaped 
sides  of  the  skull  are  formed  by  the  upper  jaw  and  other  por- 
tions of  the  visceral  skeleton. 

This  part  of  the  skull,  like  that  already  examined,  is  com- 
posed of  cartilage  and  bone,  the  cartilage  forming  the  primitive 
skull,  the  bone  being  either  cartilage  bone,  which  replaces  the 
cartilage  in  certain  places,  or  membrane  bone  which  may  cover 
or  incase  it. 

The  cranial  bones  fall  into  two  distinct  groups,  —  those  forming 
the  brain  case,  or  cranium  proper,  and  those  forming  the  capsules 
of  the  special  sense  organs.  The  primitive  cartilaginous  cranium, 
which  is  partly  replaced  or  covered  by  these  bones,  persists 
throughout  the  life  of  the  animal  in  great  part,  and  appears  on 
the  surface  in  a  number  of  places.  In  skulls  which  have  been 
allowed  to  become  dry  this  cartilage  will  have  disappeared. 

The  cranium  proper  contains  the  following  bones.  At  the 
posterior  end  of  the  skull  and  surrounding  the  foramen  mag- 
num are  the  two  exoccipital  bones ;  they  are  cartilage  bones.  Each 
exoccipital  bears  on  its  hinder  surface  a  convex  articular  pro- 
jection,—  the  occipital  condyle,  —  by  which  the. skull  articulates 
with  the  atlas.  At  the  side  of  each  exoccipital  will  be  seen  a 
portion  of  the  primitive  cartilage. 

The  pair  of  long  flat  bones  which  form  the  roof  of  the 
cranium  and  lie  directly  in  front  of  the  occipitals  are  the  fronto- 
parietal  bones ;  they  are  membrane  bones  which  lie  on  top  of  the 
primitive  cartilage.  They  may  be  raised  up  if  the  skull  has  not 
been  allowed  to  become  dry  and  the  cartilage  exposed.  Note 
the  three  large  openings  present  in  it.  The  anterior  ends  of 
the  fronto-parietals  overlap  a  bony  ring  which  encircles  the  for- 
ward end  of  the  brain  case ;  this  is  the  ethmoid,  a  cartilage  bone. 

The  ventral  portion  of  the  cranium  is  formed  by  two  bones, 
—  the  ethmoid,  just  mentioned,  and  the  parasphenoid  or  parabasal. 
The  latter  is  a  large  T-shaped  membrane  bone  which  covers 
the  entire  ventral  portion  of  the  primitive  cartilaginous  cranium 


THE  FBOG  133 

and  overlaps  the  ethmoid ;  its  lateral  portions  extend  to  the 
auditory  capsules.  At  the  sides  of  it,  back  of  the  ethmoid,  will 
be  seen  the  primitive  cartilage.  The  large  foramen  of  the  optic 
nerve  will  be  seen  in  the  side  of  the  cranium  between  the 
fronto-parietal  and  the  parasphenoid. 

The  special  sense  capsules.  These  are  the  auditory  capsules 
at  the  hinder  end  of  the  skull  and  the  nasal  capsules  at  its  for- 
ward end.  The  optic  capsules  do  not  ossify;  they  are  largely 
membranous,  with  delicate  cartilaginous  plates  in  the  solera. 

The  auditory  capsules  are  fused  with  the  sides  of  the  cranium 
proper  and  consist  largely  of  cartilage.  On  the  ventral  side  of 
the  skull  the  lateral  projections  of  the  parasphenoid  bone  cover 
them.  On  the  dorsal  and  anterior  sides  a  cartilage  bone  called 
the  prootic  is  present ;  it  will  be  seen  abutting  the  hinder  part  of 
the  fronto-parietal  bone.  Between  the  prootic  and  parasphenoid 
bones  is  the  large  foramen  of  the  trigeminal  nerve. 

Ventral  to  the  prootic  on  the  side  of  the  skull  is  a  depression; 
at  the  bottom  of  this  is  a  large  hole  called  the  fenestra  ovalis, 
which  looks  inside  the  auditory  capsule.  The  depression  is  the 
tympanic  cavity,  —  the  middle  ear  of  higher  vertebrates,  —  which 
in  the  fresh  skull  is  covered  laterally  by  the  tympanic  membrane, 
or  ear  drum.  The  fenestra  ovalis  is  closed  by  a  minute  carti- 
lage called  the  operculum,  which,  in  turn,  is  joined  with  the  tym- 
panic membrane  by  a  small  bony  and  cartilaginous  rod  called 
the  columella.  These  two  small  structures,  like  the  ossicles 
of  the  mammalian  ear,  convey  the  sound  waves  from  the  tym- 
panic membrane  to  the  inner  ear.  Skulls  from  which  the 
tympanic  membrane  has  been  removed  have  often  lost  them. 

The  two  nasal  capsules  lie  side  by  side,  fused  with  the  anterior 
end  of  the  cranium  proper,  and  are  also  composed  largely  of 
cartilage.  The  ringlike  ethmoid  bone,  which,  as  we  have  seen, 
forms  the  anterior  end  of  the  brain  case,  also  forms  the  poste- 
rior end  of  the  nasal  capsules.  Two  pairs  of  membrane  bones 
are  present  in  these  capsules,  the  dorsal  nasals  and  the  ventral 
vomers.  The  former  are  a  pair  of  large  bones  which  lie  in  a  trans- 
verse position  covering  the  cartilage  just  in  front  of  the  ethmoid ; 
the  latter  are  a  pair  of  bones  also  in  front  of  the  ethmoid,  on 


134  VERTEBRATE  ZOOLOGY 

the  ventral  surface  of  the  skull,  each  bone  bearing  a  group  of 
small  teeth. 

The  upper  jaw  and  the  other  remaining  portions  of  the  visceral 
skeleton  still  remain  to  be  described.  The  upper  jaw  forms 
two  distinct  arches,  an  outer  or  maxillary  arch,  and  an  inner  or 
palatopterygoid  arch,  —  the  former  consisting  of  three  and  the 
latter  of  two  membrane  bones  on  each  side. 

The  three  bones  of  the  maxillary  arch,  on  each  side,  are  the 
quadratojugal,  the  small  posterior  bone;  the  maxillary,  the  long 
thin  bone  which  bears  most  of  the  teeth ;  and  the  premaxillary, 
the  small  anterior  bone  which  forms  the  anterior  end  of  the 
skull  and  also  bears  teeth. 

The  two  bones  of  the  palatopterygoid  arch,  on  each  side,  are 
the  pterygoid  and  the  palatine.  The  former  is  a  large  bone  which 
lies  at  the  hinder  end  of  the  skull,  medial  to  the  quadratojugal 
and  the  maxillary,  and  is  best  seen  on  the  ventral  surface.  It 
has  three  ends,  —  its  forward  end  going  to  the  maxillary  bone, 
its  hinder  end  to  the  quadratojugal,  and  its  medial  end  to  the 
parasphenoid.  The  palatine  is  a  slender  bone  which  lies  on  the 
ventral  surface  and  extends  from  the  maxillary  at  the  forward 
end  of  the  pterygoid  transversely  to  the  ethmoid. 

The  bones  and  cartilages  by  which  the  lower  jaw  is  suspended 
from  the  cranium  are  called  the  suspensorium.  In  the  frog  it  is 
formed  on  each  side  by  a  small  cartilage,  —  the  quadrate,  —  and  a 
membrane  bone,  —  the  paraquadratum  or  squamosal.  The  quadrate 
lies  at  the  extreme  latero-posterior  end  of  the  skull,  in  close 
connection  with  the  quadratojugal  bone  and  between  the  ptery- 
goid and  squamosal;  the  lower  jaw  articulates  with  its  outer 
surface.  The  squamosal  is  a  T-shaped  bone  which  lies  on  the 
dorsal  surface  of  the  skull  in  the  region -of  the  auditory  capsule; 
it  supports  the  tympanic  membrane. 

Exercise  36.  Draw  a  view  of  the  dorsal  aspect  of  the  skull. 
Show  accurately  the  outlines  of  the  bones  and  cartilages, 
and  indicate  by  a  difference  in  color  or  by  shading  which 
are  cartilage  bones  and  which  are  membrane  bones. 

Exercise  37.  Draw  a  similar  view  of  the  ventral  aspect. 


CHAPTER   III 
REPTILES 
A  TURTLE 

Many  species  of  land  and  fresh-water  turtles  occur  in  the 
eastern  and  central  United  States.  The  following  table  will  aid 
in  identifying  most  of  the  common  species.1 

Ar  Turtles  with  shell  poorly  ossified ;  body  covered  with  a  leathery  skin 

in  which  scales  are  lacking. 

Aspidonectes  spinifer,  the  soft-shell  turtle.  Carapace  round,  spotted ;  plas- 
tron nearly  white;  legs  and  feet  mottled;  nostrils  terminal; 
aquatic. 

Amy  da  mutica,  the  leather  turtle.    A  depression  along  median  line  of 
carapace;  nostrils  not  terminal;  in  Great  Lakes  and  upper  Mis- 
sissippi. 
A2.  Turtles  with  well-ossified  carapace;  scales  present  in  skin. 

1.  Family  Testudinidce.     Carapace  strongly  arched;  plastron  broad  and 

composed  of  12  plates ;  toes  joined  by  skin,  only  the  blunt  claws 
projecting. 

Testudo  Carolina,  the  Carolina  gopher  of  the  Southern  States  ;  burrows 
in  the  ground. 

2.  Family  Kinosternidce.    Plastron  large,  with  7,  9,  or  11  plates. 

ar  Kinosternum  pennsylvanicum,  the  small  mud  turtle.  Shell  dusky 
brown  ;  head  dark,  with  light  spots ;  aquatic,  but  also  found  on  the 
land  ;  not  so  common  as  the  following  species ;  length  4  inches. 

«2.  Aramochelys  odorata,  the  musk  turtle.  Shell  dusky,  sometimes 
spotted ;  neck  with  two  yellow  stripes  on  each  side ;  with  odor  of 
musk  ;  aquatic  and  common  ;  length  6  inches. 

3.  Family  Emydce.    Plastron  with  12  plates. 

ar  Chelopus  guttatus,  the  spotted  turtle.    Black,  with  yellow  spots ; 

aquatic. 
a2.  Chelopus  insculptus,  the  wood  turtle.     Carapace  with  keel,   its 

plates  marked  with  concentric  striae ;  both  terrestrial  and  aquatic. 
as.   Chrysemys  picta,  the  painted  turtle.   Greenish  black  ;  plates  edged 

with  yellow ;  marginal  plate  marked  with  red ;  aquatic. 
o4.   Cistudo  Carolina,  the  box  turtle.    Yellowish  brown,  with  blotches 

of  yellow ;  plastron  with  hinge ;  terrestrial. 

4.  Family  Clielydridce.    Plastron  small,  with  9  plates. 

Chelydra  serpentina,  the  snapping  turtle.  Length  up  to  3  feet;  aquatic. 

1  These  descriptions  have  been  modified  from  Bulletin  No.  51  of  the  New 
York  Museum. 

135 


136  VEETEBEATE  ZOOLOGY 

Two  specimens  will  be  needed  for  a  complete  dissection,  —  one 
for  the  study  of  the  outer  form,  the  viscera  including  the  heart  and 
the  main  blood  vessels,  the  sympathetic  and  spinal  nerves,  and  the 
skeleton,  and  one  for  the  brain  and  cranial  nerves  and  the  smaller 
blood  vessels.  The  sex  of  the  turtle  may  usually  be  determined 
by  the  condition  of  the  plastron,  which  in  the  male  is  flat  or 
concave,  and  in  the  female  slightly  convex.  The  animal  may 
be  killed  by  being  placed  under  a  bell  jar  together  with  a  wad 
of  cotton  soaked  with  chloroform  or  ether :  several  hours  may 
elapse  before  it  is  dead. 

Observe  the  form  and  color  of  the  animal;  note  if  the  color 
markings  are  bilaterally  symmetrical.  Turtles  are  sharply  dis- 
tinguished from  other  vertebrates  by  the  possession  of  a  hard 
case  or  shell  within  which  the  animal  can  withdraw  the  head, 
tail,  and  legs  more  or  less  completely.  The  shell  is  composed  of 
flattened  plates  of  bone  overlaid  by  thin  plates  of  horn  (tortoise 
shell),  and  is  made  up  of  two  distinct  portions,  —  the  dorsal  con- 
vex carapace,  and  the  ventral,  flattened  plastron.  In  some  turtles 
these  two  parts  of  the  shell  are  not  in  contact  with  each  other, 
while  in  others  they  are  joined  at  the  sides  of  the  body. 

The  horny  plates  forming  the  outer  surface  of  the  carapace 
fall  into  several  longitudinal  rows.  In  most  turtles  the  middle 
row  consists  of  five  neural  and  one  nuchal  plate  ;  the  latter  is  the 
foremost  one  in  the  row,  and  is  wanting  in  some  turtles.  Lateral 
to  this  row  on  each  side  are  four  costal  and  twelve  marginal  plates. 
The  posterior  pair  of  marginals  often  become  fused  and  form 
the  unpaired  pygal  plate. 

The  plastron  is  usually  covered  by  two  rows  of  horny  plates, 
with  an  additional  pair  on  the  bridge  joining  the  carapace  and 
plastron  on  each  side. 

In  certain  species  of  turtles  concentric  lines  of  growth  may 
be  seen  in  the  horny  plates  of  the  shell,  each  ring  representing 
a  year's  growth.  The  central  nucleus  of  the  plate  shows  its 
size  when  the  animal  was  born. 

Note  the  looseness  of  the  skin  of  the  neck,  legs,  and  tail, 
which  enables  them  to  be  drawn  under  the  shell.  If  scales  are 
present  in  the  skin,  note  their  variation  in  size. 


A  TURTLE  137 

The  body  of  the  turtle  may  be  divided  into  four  regions,  — 
the  head,  neck,  trunk,  and  tail.  In  most  turtles  the  soft  parts  of 
all  these  regions  are  covered  by  horny  scales  which  are  similar 
in  texture  to  the  outer  plates  of  the  shell. 

The  hea*d  is  compactly  and  very  strongly  built,  with  powerful 
jaws  which  are  armed  with  horny  plates  instead  of  teeth,  and 
contrasts  markedly  with  the  heads  of  amphibians  and  fishes. 
The  mouth  is  ventral  in  position,  and  projecting  in  front  of  it  is 
the  snout,  with  the  paired  nostrils  or  anterior  nares  at  its  forward 
end.  The  eyes  are  prominent  objects ;  they  do  not  usually  pro- 
ject from  the  head,  but  are  protected  above  and  below  by  bony 
ridges  of  the  skull.  Each  is  provided  with  three  eyelids, — the 
thick  upper  lid,  the  more  movable  lower  lid,  and  the  nictitating 
membrane,  —  a  translucent  third  lid  which  can  be  withdrawn  into 
the  anterior  corner  of  the  eye.  Just  back  of  the  mouth  is  a 
slight  circular  depression  which  marks  the  position  of  the  tym- 
panic membrane,  or  ear  drum,  which  lies  on  the  outer  surface  of 
the  head  as  it  does  in  the  frog. 

The  neck  of  the  turtle  is  very  long  and  flexible,  a  feature 
which  is  correlated  with  the  heavy,  awkward  trunk. 

The  trunk  is  inclosed  within  the  shell  and  bears  the  extremities. 
It  shows  a  high  degree  of  specialization.  The  spinal  column  and 
ribs  have  become  flattened  and  help  to  form  the  shell,  and  the 
trunk  muscles  are  wanting.  Two  pairs  of  appendages  are  pres- 
ent. Each  leg  is  made  up  of  three  divisions,  a  proximal,  a  middle, 
and  a  terminal  division,  which  correspond  to  the  upper  arm,  the 
forearm,  and  the  wrist  and  hand  in  the  fore  leg,  and  in  the  hind 
leg  to  the  thigh,  the  shank,  and  the  ankle  and  foot.  Identify  these 
divisions.  Note  the  absence  of  a  sole  or  walking  surface  on  the 
feet ;  note  the  number  of  toes  on  each  foot,  and  the  claw  on  each 
toe.  See  if  the  toes  are  free  or  are  joined  by  a  membrane. 

The  tail  is  usually  short  and  conical,  and  bears  on  its  under 
side  the  anus,  the  opening  of  the  cloaca.  Note  if  the  tail  can  be 
withdrawn  under  the  shell. 

Exercise  i.  Make  a  drawing  of  the  carapace,  showing  accurately 
the  outlines  of  the  horny  plates,  and  label  them. 


138  VERTEBRATE   ZOOLOGY 

Exercise  2.  Make  a  similar  drawing  of  the  plastron. 

Exercise  3.  Draw  a  side  view  of  the  head  on  the  scale  of  2, 
showing  accurately  the  outlines  of  the  scales ;  label  all 
the  organs. 

The  mouth  and  pharynx.  Open  the  mouth  and  disarticulate 
the  lower  jaw,  after  cutting  the  angle  on  each  side.  The  mouth 
and  pharynx  form  a  single  space;  of  this  the  pharynx  is  the 
hinder  part,  where  the  course  of  the  air  from  the  nostrils  to  the 
lungs  crosses  that  of  the  food  from  the  mouth  to  the  stomach. 
Observe  the  form  and  arrangement  of  the  plates  covering  the 
jaws.  Find  the  posterior  nares,  the  inner  opening  of  the  nostrils. 
Observe  the  floor  of  the  mouth  ;  note  the  shape  and  character  of 
the  tongue,  and  the  opening  of  the  glottis  just  behind  it,  through 
which  air  is  admitted  into  the  trachea  and  the  lungs.  Probe  the 
glottis  and  note  the  two  arytenoid  cartilages  which  guard  the 
opening  and  form  a  part  of  the  larynx.  Place  a  blowpipe  in* 
the  glottis  and  inflate  the  lungs. 

Exercise^*.  Draw  two  sketches,  —  one  of  the  floor  and  one  of 
the  roof  of  the  mouth,  on  a  scale  of  3. 

The  internal  organs.  Open  the  body  cavity  in  the  following 
manner.  Saw  or  cut  through  the  bridge  connecting  the  cara- 
pace and  the  plastron  on  each  side,  taking  care  not  to  cut  too 
deeply.  Then  with  the  scalpel  or  scissors  cut  the  skin  where  it 
is  attached  to  the  plastron,  both  in  front  and  behind.  Placing 
then  the  animal  on  its  back,1  carefully  raise  the  plastron  at  the 
forward  end,  and  with  a  scalpel  cut  the  muscles  where  they 
are  attached  to  its  inner  surface.  Care  must  be  taken  to  keep 
the  blade  at  all  times  close  to  the  plastron  in  order  to  avoid 
cutting  the  organs  within.  Remove  the  plastron,  first  noticing 
the  glistening  fibrous  periosteum  and  the  muscle  attachments  on 
its  inner  surface. 

Observe  the  ventral  aspect  of  the  animal.  A  tough  mem- 
brane—  the  peritoneum — will  be  seen  covering  the  body  cavity, 

1  If  a  towel  be  rolled  up  lengthwise  and  the  roll  be  made  into  a  ring,  a  stable 
support  will  be  obtained  to  rest  the  animal  upon  during  the  dissection. 


A  TURTLE  139 

within  which  the  viscera  will  be  indistinetly  visible.  The  body 
cavity  is  divided  into  two  compartments, —  the  abdominal  cavity 
and  the  pericardial  cavity.  The  former  is  the  larger  and  contains 
the  liver,  intestine,  and  most  of  the  other  viscera ;  it  is  lined  by 
a  membrane  called  the  peritoneum.  The  latter  contains  only  the 
heart  and  the  base  of  the  great  blood  vessels ;  it  is  formed  by  a 
membrane  called  the  pericardium. 

It  will  be  observed  that  no  abdominal  muscles  are  present, 
which  in  other  land  vertebrates  form  the  ventral  and  lateral 
walls  of .  the  abdomen;  this  feature  is  correlated  with  the  pres- 
ence of  the  shell.  At  the  forward  end  are  the  large  pectoral 
muscles;  they  cover  the  ventral  portion  of  the  pectoral  girdle, 
the  bony  structure  which  supports  the  fore  legs.  At  the  hinder 
end  are  the  large  pelvic  muscles,  which  cover  the  pelvis,  —  the 
structure  supporting  the  hind  legs.  Both  pectoral  and  pelvic 
girdles  may  be  felt  through  these  muscles.  Imbedded  in  the 
muscles  and  the  peritoneum  may  be  seen  the  yellow  fat. 
Within  the  pericardium  will  be  seen  the  heart. 

Imbedded  in  the  peritoneum  are  the  two  prominent  abdominal 
veins  running  in  a  diagonally  longitudinal  direction,  and  joined 
together  by  cross  veins.  It  will  be  remembered  that  in  amphib- 
ians a  single  median  abdominal  vein  is  present. 

Exercise  5.  Make  a  semidiagrammatic  sketch  of  the  ventral 
aspect  of  the  animal,  showing  these  organs,  and  carefully 
label  all. 

With  sharp  scissors  cut  away  the  entire  ventral  portion  of 
the  peritoneum  and  pericardium,  together  with  the  muscles  at- 
tached to  them.  Note  carefully  where  the  abdominal  veins  leave 
the  peritoneum  and  go  to  the  liver.  Do  not  cut  the  heart  or  any 
of  the  other  organs  in  the  body  cavity. 

Observe  the  organs  as  they  lie  in  the  body  cavity  in  their 
natural  positions.  Just  back  of  and  beneath  the  pectoral  muscles 
is  the  heart,  and  back  of  and  at  the  sides  of  it  is  the  large  liver, 
the  largest  organ  present.  The  liv«r  consists  of  a  right  and  a 
left  lobe  joined  by  a  narrow  bridge.  Near  the  posterior  edge  of 
the  right  lobe  may  be  seen  the  green  gall  bladder.  Partly  or 


140  VERTEBRATE  ZOOLOGY 

wholly  beneath  the  outer  edge  of  the  left  lobe  and  joined  with 
it  by  a  mesentery  is  the  U-shaped  stomach;  while  back  of  the 
liver  are  the  coils  of  the  intestine. 

Lift  up  the  intestine  gently  and  note  the  membranous  mesen- 
tery which  joins  it  with  the  dorsal  body  wall  and  holds  it  in 
place.  All  the  organs  in  the  abdominal  cavity  are  thus  sup- 
ported by  mesenteries,  which  are  folds  of  the  peritoneum. 

In  the  posterior  portion  of  the  abdominal  cavity  are  the  uro- 
genital  organs.  If  the  animal  be  a  male,  the  spheroid  testes, 
which  are  usually  of  a  yellow  or  reddish  color,  and  the  black 
epididymis  which  lies  alongside  and  back  of  each  one,  will  be 
seen.  If  a  female,  the  granular,  yellow  ovaries  and  the  tubular, 
convoluted  oviducts  will  be  seen.  The  condition  and  extent  of 
these  organs  are,  however,  dependent  upon  the  sexual  condi- 
tion of  the  animal.  The  kidneys  are  dark-red  organs  which  lie 
against  the  dorsal  body  wall  and  will  not  yet  be  seen.  At  the 
hinder  end  of  the  abdominal  cavity  is  the  large  bilobed  urinary 
bladder,  and  back  of  it,  beneath  the  pelvis,  is  the  cloaca,  which 
leads  to  the  anus. 

The  large  lungs  are  often  visible  in  the  abdominal  cavity. 
They  may  always  be  brought  into  view  by  blowing  into  the 
glottis  through  a  blowpipe. 

Exercise  6.  Make  an  outline  drawing  of  the  ventral  aspect  of  the 
animal,  showing  the  viscera  as  they  lie  in  the  body  cavity. 

The  heart  and  its  vessels.  Carefully  dissect  away  what  re- 
mains of  the  ventral  wall  of  the  pericardium  and  the  pectoral 
muscles,  so  as  to  bring  into  view  the  forward  portion  of  the 
heart  and  the  arteries  springing  from  it. 

The  heart  is  made  up  of  the  transversely  elongated  ventricle, 
the  two  auricles,  and  the  sinus  venosus.  The  ventricle  has  thick 
muscular  walls,  and  hence  is  usually  not  so  deep  red  as  the 
thinner-walled  auricles  and  the  sinus  venosus.  The  auricles 
appear  one  on  each  side  of  the  forward  end  of  the  ventricle. 
The  ventricle  is  divided  internally  by  a  partial  septum  into 
two  chambers  which  communicate  with  each  other.  Springing 
from  its  anterior  border  are  the  following  arterial  trunks :  a 


A  TURTLE  141 

right  and  a  left  aorta,  an  innominate  artery,  and  a  pulmonary  artery. 
Directly  in  front  of  these  in  the  median  line  will  be  seen  the 
small  round  thyroid  gland;  the  trachea,  or  windpipe,  may  also  be 
seen,  and  may  be  identified  by  its  cartilaginous  rings. 

Of  the  arterial  trunks  the  one  which  appears  on  the  animal's 
right  in  the  ventral  aspect  is  the  innominate  artery.  It  branches 
almost  immediately  into  the  right  and  left  subclavian  and  the  right 
and  left  carotid  arteries.  Each  subclavian,  after  giving  off  branches 
to  the  thyroid  gland  and  the  neck,  becomes  the  axillary  artery;  this 
artery  gives  off  branches  to  the  pectoral  muscles  and  finally  as 
the  brachial  artery  enters  the  leg.  The  carotids  pass  along  the 
neck  to  the  head. 

Next  to  the  innominate  artery  is  the  left  aorta,  which  springs 
from  the  right  side  of  the  ventricle,  passes  to  the  left  side  of  the 
body,  turns  dorsally  and  posteriorly,  and  finally  joins  the  right 
aorta  just  beneath  the  spinal  column,  forming  thus  the  dorsal 
aorta.  The  right  aorta  lies  behind  the  innominate  and  will  not 
be  seen  at  present ;  it  springs  from  the  left  side  of  the  ventricle 
and  passes  to  the  right  side  of  the  body  to  aid  in  forming  the 
dorsal  aorta. 

At  the  left  of  the  aorta  is  the  pulmonary  artery.  It  divides  im- 
mediately into  a  right  and  a  left  pulmonary,  which  go  to  the  lungs. 

These  vessels  will  be  studied  in  greater  detail  when  the  whole 
vascular  system  is  dissected. 

The  thymus  gland —  a  small,  loose,  yellowish  mass  of  tissue  — 
will  be  seen  on  each  side  lying  dorsal  to  and  in  contact  with 
the  arterial  trunks  a  short  distance  from  the  heart. 

Exercise  7.  Draw  the  ventral  aspect  of  the  heart  and  the  arterial 
trunks  and  their  branches  so  far  as  they  have  been  observed. 

4 

Bend  the  heart  forward  and  pin  it  there.  Observe  the  right 
and  left  auricles ;  also  the  large  sinus  venosus,  which  is  a  large 
dark-colored  vessel  extending  across  the  pericardial  space  and 
opening  into  the  right  auricle.  Four  large  veins  enter  the 
sinus,  bringing  blood  to  the  heart,  —  the  right  and  left  precaval 
veins,  which  bring  blood  from  the  forward  part  of  the  body; 
the  left  hepatic  vein,  from  the  left  lobe  of  the  liver;  and  the 


142  VERTEBRATE  ZOOLOGY 

postcaval  vein,  which  brings  blood  from  the  hinder  part  of  the 
body  and  the  right  lobe  of  the  liver. 

Observe  the  large  pulmonary  vein,  which  brings  arterial  blood 
to  the  left  auricle  from  the  lungs.  It  is  formed  by  the  union 
of  a  right  and  a  left  pulmonary,  each  of  which  may  be  seen  lying 
alongside  the  bronchus  on  each  side ;  the  bronchi  are  the  two 
large  branches  into  which  the  trachea  divides. 

Exercise  8.  Draw  the  dorsal  aspect  of  the  heart  diagrammatically 
and  the  base  of  the  great  veins  entering  it. 

The  internal  structure  of  the  heart.  Cut  the  great  vessels 
entering  and  leaving  the  heart  a  short  distance  from  their  base 
and  remove  the  heart  from  the  body.  Place  it  in  water,  with 
the  dorsal  side  uppermost.  Open  the  sinus  venosus  and  wash 
out  the  blood  in  it.  Note  its  thin  walls.  Find  -the  large  open- 
ing into  the  right  auricle  and  the  two  valves  guarding  it.  Care- 
fully open  the  auricles  by  carrying  a  slit  around  their  anterior 
edge  and  wash  out  the  blood.  Note  the  thin  septum  between 
the  auricles,  and  the  ridges  in  their  walls.  Pass  a  probe  from 
the  sinus  venosus  into  the  right  auricle.  Observe  the  opening 
from  each  auricle  into  the  ventricle,  one  being  on  each  side  of 
the  septum.  Probe  them. 

Cut  open  the  ventricle  by  carrying  a  slit  along  its  anterior 
end  through  the  auricular  openings.  Note  its  small  cavity  and 
the  incomplete  septum  which  divides  it  into  two  communicat- 
ing spaces;  note  also  the  great  thickness  of  the  walls  of  the 
ventricle  and  the  muscle  ridges  which  project  into  the  cavity. 
Find  the  openings  of  the  large  arteries  into  the  ventricle  by 
probing  through  them  into  it.  Note  that  the  pulmonary  artery 
and  the  left  aorta  arise  in  the  right  side,  and  the  right  aorta  and 
the  innominate  artery  arise  in  the  left  side  of  the  ventricle. 
Find,  by  using  the  blowpipe,  the  valves  which  guard  the  mouths 
of  all  these  arteries.  The  circulation  of  the  blood  in  the  heart 
goes  on  as  follows.  Blood  is  brought  to  the  heart  .by  the  caval 
veins  and  the  pulmonary  vein,  The  former  bring  venous  blood 
from  the  various  organs  and  tissues  of  the  body  to  the  sinus 
venosus,  from  which  it  goes  to  the  right  auricle  to  be  pumped 


A  TUKTLE  143 

finally  into  the  right  side  of  the  ventricle.  The  pulmonary  vein 
brings  arterial  blood  from  the  lungs  to  the  left  auricle,  from 
which  it  is  pumped  into  the  left  side  of  the  ventricle.  The 
ventricle  thus  receives  both  kinds  of  blood,  but  the  incomplete 
septum  and  the  muscle  ridges  serve  to  prevent  a  complete 
mingling  of  them. 

Blood  leaves  the  heart  by  the  four  great  arteries  which  take 
their  rise  in  the  anterior  end  of  the  ventricle.  The  two  leav- 
ing the  right  side  of  the  ventricle  —  the  pulmonary  and  the  left 
aorta —  carry  blood  which  is  predominantly  venous ;  this  blood 
is  carried  by  the  pulmonary  artery  to  the  lungs,  and  by  the  left 
aorta  largely  to  the  stomach  and  intestine.  The  two  arteries 
leaving  the  left  side  of  the  ventricle  carry  blood  which  is  pre- 
dominantly arterial  to  the  remaining  tissues  and  organs  of  the 
body. 

Exercise  9.  Draw  a  diagram  showing  the  internal  structure  of 
the  heart  so  far  as  observed. 

The  digestive  system.  This  system  is  composed  of  the  fol- 
lowing organs :  the  mouth,  pharynx,  oesophagus,  stomach,  small 
intestine,  large  intestine,  and  cloaca,  and  the  liver  and  pan- 
creas,—  two  large,  glandular  organs  which  communicate  with 
the  small  intestine. 

With  a  scalpel  cut  through  the  pelvis  in  the  median  line. 
Inasmuch  as  the  pelvic  bones  of  the  right  and  left  sides  are 
united  in  the  median  line  by  a  cartilaginous  symphysis,  this 
will  be  easily  done.  Pull  the  two  halves  of  the  pelvis  as  far 
apart  as  possible  1  and  separate  the  tissues  beneath,  thus  expos- 
ing the  cloaca. 

Observe  the  extent  of  the  cloaca.  It  will  be  seen  to  be  a 
muscular  tube  passing  beneath  the  pelvis.  At  its  anterior  end 
it  is  continuous  with  the  rectum,  the  posterior  division  of  the 

1  The  pectoral  and  pelvic  girdles  may  be  conveniently  kept  out  of  the  way 
while  the  dissection  of  the  viscera  is  progressing  as  follows  :  Tie  a  stout  string 
around  the  right  pelvic  girdle,  pass  it  back  over  the  carapace  to  the  left  pectoral 
girdle,  then  over  the  carapace  to  the  right  pectoral  girdle  and  back  again 
over  the  carapace  to  the  left  pelvic  girdle.  Pull  it  as  tight  as  possible  around 
all  of  these  girdles  and  fasten  it  to  the  last  one. 


144  VERTEBRATE  ZOOLOGY 

i 
large  intestine.    The  large  urinary  bladder  is  joined  with  its 

ventral  wall  by  a  narrow  neck.  The  urinary  and  genital  ducts 
join  its  dorsal  wall,  and  the  penis,  in  the  male,  is  a  specialized 
portion  of  its  ventral  wall. 

Turn  the  liver  forward  and  note  the  stomach  beneath  its  left 
border.  The  anterior  end  of  the  stomach,  where  the  oesophagus 
joins  it,  is  the  cardiac  end ;  its  posterior  end,  where  it  opens  into 
the  small  intestine,  is  the  pyloric  end,  and  is  marked  by  a  con- 
striction. The  anterior  end  of  the  small  intestine,  which  lies  be- 
tween the  pylorus  and  the  bile  duct,  is  called  the  duodenum. 
Note  the  gall  bladder  in  the  right  lobe  of  the  liver,  and  the  bile 
duct  which  joins  it  with  the  duodenum.  The  green  bile  may 
often  be  squeezed  into  this  duct  from  the  gall  bladder.  Note 
the  pancreas,  a  pinkish  organ  which  extends  along  the  duode- 
num, and  the  pancreatic  duct  which  joins  it  with  the  duodenum. 

Exercise  10.  Draw  the  dorsal  aspect  of  the  liver,  together  with 
the  stomach,  duodenum,  and  pancreas. 

Cut  the  intestine  loose  from  its  mesentery  as  far  forward  as 
the  bile  duct,  which  must  be  preserved.  Do  this  by  lifting  the 
intestine  up  with  forceps  and  cutting  the  mesentery  where  it 
joins  it.  Note  the  great  length  of  the  small  intestine.  The 
large  intestine  contains  three  divisions,  —  the  caecum,  a  short, 
thick,  blind  gut  at  its  forward  end,  and  the  colon  and  the  rectum 
which  form  the  greater  part  of  it.  The  rectum  is  sometimes 
wider  than  the  colon  and  is  continuous  posteriorly  with  the 
cloaca.  Lying  near  the  colon  in  the  mesentery  is  the  dark-red 
spleen ;  it  is  not  a  part  of  this  system. 

Free  the  liver  from  its  connection  with  the  lungs  and  other 
organs  which  lie  dorsal  to  it,  but  be  careful  not  to  cut  the  bile 
duct.  Cut  the  mesentery  which  joins  the  stomach  with  the  liver. 
Observe  the  cardiac  end  of  the  stomach  and  the  ceosophagus.  Follow 
the  latter  to  the  head.  Stretch  out  the  digestive  tract  on  the  dis- 
secting^ board,  with  the  liver  and  pancreas  still  attached  to  it. 

Exercise  11.  Make  a  drawing  of  the  entire  digestive  tract,  show- 
ing the  relative  lengths  of  the  different  divisions ;  carefully 
label  all. 


A  TURTLE  145 

>  I     ;. 

Cut  the  rectum  and  the  oesophagus  and  remove  the  digestive 
tract.  Slit  open  the  rectum  and  £h£  colon,  also  the  stomach  and 
the  duodenum,  and  observe  the  folds  of  the  mucous  membrane. 

The  respiratory  system.  The  large  lungs  have  already  been 
noticed  lying  against  the  inner  surface  of  the  carapace.  Observe 
their  exact  extent.  From  each  lung  a  tube  called  the  bronchus 
passes  ventrally  and  anteriorly,  the  two  bronchi  joining  to  form 
the  trachea,  or  windpipe.  Note  the  cartilaginous  rings  which  pre- 
vent the  bronchi  and  the  trachea  from  collapsing.  Trace  the 
trachea  forward  to  the  glottis,  its  opening  into  the  pharynx. 

The  forward  end  of  the  trachea  is  formed  by  the  larynx ;  this 
contains  a  number  of  cartilages  and  has  for  its  principal  func- 
tion the  control  of  the  passage  of  air  into  and  out  of  the  lungs. 
In  the  turtle  it  is  composed  of  a  large  posterior  cartilaginous  ring, 
the  crico-thyroid  cartilage,  and  a  pair  of  small  cartilages,  the  aryte- 
noids,  which  guard  the  opening  of  the  glottis.  Cut  open  a  lung 
and  examine  its  inner  texture.  Note  the  large  open  spaces  in  it. 

Exercise  12.  Draw  a  diagram  showing  the  respiratory  system. 

The  urogenital  system.  Observe  the  cloaca  passing  to  the  anus; 
observe  the  rectum  and  the  bladder.  Cut  a  hole  in  the  bladder 
and  probe  through  it  into  the  cloaca.  Probe  through  the  anus 
into  the  bladder. 

If  the  animal  be  a  male,  note  the  large  penis  in  the  cloaca. 
Widen  the  opening  of  the  anus,  if  necessary,  and  observe  that 
the  penis  is  a  specialized  portion  of  the  ventral  cloacal  wall. 
Note  the  groove  along  the  middorsal  surface  of  the  penis  and 
the  enlargement  at  its  free  end. 

Free  the  bladder  from  its  attachments  with  the  surrounding 
organs,  but  do  not  sever  its  connection  with  the  cloaca.  Raise 
the  bladder  and  observe  the  two  yellow  testes,  and  beside  and 
behind  each  the  black  epididymis,  which  is  the  terminal  portion 
of  the  vas  deferens.  Trace  the  vas  deferens  to  the  cloaca.  Lift 
up  the  testis  with  forceps  and  observe  the  vasa  efferentia,  the  fine 
tubes  which  connect  it  with  the  epididymis. 

If  the  animal  be  a  female,  the  paired  ovaries  will  be  seen  in 
the  hinder  part  of  the  body  cavity,  filled  with  the  round,  yellow 


146  VERTEBRATE  ZOOLOGY 

ova.  A  pair  of  oviducts  is  present,  one  on  each  side  of  the  median 
line.  Each  oviduct  is  a  long  tube  which  opens  posteriorly  into 
the  cloaca;  its  posterior  end  is  enlarged,  forming  a  uterus.  Its 
anterior  end  opens  by  a  broad  mouth  into  the  body  cavity. 
Straighten  out  one  of  the  oviducts,  cutting  the  fold  of  the  peri- 
toneum in  which  it  lies.  Find  its  mouth ;  if  it  is  hard  to  find, 
cut  a  hole  in  it  and  probe  forward.  In  a  similar  way  probe 
backward  into  the  cloaca. 

Exercise  13.  Make  a  semidiagrammatic  drawing  of  the  genital 
organs. 

Remove  the  genital  organs.  The  dark-red  kidneys  will  be 
exposed  lying  close  to  the  dorsal  body  wall.  Along  the  median 
border  of  each  is  an  elongated  yellow  patch,  —  the  suprarenal 
bodies.  Trace  the  short  ureter  to  the  cloaca  on  each  side.  It  is 
formed  by  the  union  of  a  number  of  ducts  on  the  ventral  sur- 
face of  the  kidney.  Note  the  exact  point  where  the  ureter  joins 
the  kidney.  Slit  open  the  entire  cloaca  and  note  the  mouths 
of  the  ureters  and  the  genital  ducts. 

Exercise  14.  Make  a  drawing  of  the  urinary  organs. 

Remove  the  lungs  and  the  urogenital  organs  from  the  body. 
Observe  the  great  retractor  muscles   of  the  head  and  neck  by 
means  of  which  these  structures  may  be  drawn  under  the  shell. ;; 
Observe  those  of  the  pelvis. 

The  nervous  system.  This  system  is  made  up  of  the  follow- 
ing parts :  (1)  the  central  nervous  system,  consisting  of  the  brain 
and  the  spinal  cord  ;  (2)  the  peripheral  nervous  system,  consisting 
of  (a)  the  paired  cranial  and  spinal  nerves  which  spring  from 
the  central  nervous  system  and  join  it  with  the  sense  organs, 
muscles,  and  other  organs,  and  (b)  the  sympathetic  nervous  sys- 
tem, which  lies,  for  the  most  part,  in  the  body  cavity  and  is 
connected  by  branches  with  the  spinal  nerves  and  with  the 
various  viscera;  and  (3)  the  organs  of  special  sense.  • 

We  shall  study  first  the  spinal  nerves  and  the  sympathetic  nerv- 
ous system.  The  spinal  nerves  spring  from  the  spinal  cord  and 


A  TURTLE  147 

• 

pass  through  the  inter  vertebral  foramina  of  the  spinal  column 
to  the  muscles  of  the  neck  and  trunk  and  the  inner  surface  of 
the  carapace.  The  sympathetic  nervous  system  consists  of  a 
pair  of  longitudinal  nerves  lying  one  on  each  side  of  the  spinal 
column,  each  nerve  containing  ganglia  at  intervals  correspond- 
ing to  the  spinal  nerves.  Branch  nerves  connect  each  ganglion 
with  a  spinal  nerve,  and  others  pass  to  the  various  viscera. 

Note  the  spinal  nerves,  which  extend  as  white  threads  across 
the  inner  surface  of  the  carapace  from  the  vertebral  column  to 
its  outer  border.  Six  or  seven  pairs  will  be  seen.  Each  nerve 
consists  of  two  main  strands  lying  side  by  side.  The  spinal 
nerves  of  the  neck,  with  the  exception  of  the  first  pair,  may 
be  seen  by  pushing  aside  the  retractor  muscles  on  the  neck. 
The  posterior  four  or  five  pairs  of  cervical  nerves  form,  together 
with  a  branch  from  the  first  spinal  nerve  of  the  trunk,  the 
brachial  plexus,  a  network  of  nerves  from  which  arise  the  nerves 
which  supply  the  fore  leg. 

Look  for  the  sympathetic  nerves  on  the  sides  of  the  great 
retractor  muscles  of  the  head  and  neck  and  on  the  surface  of 
the  vertebral  column.  The  delicate  white  cord  will  be  seen  on 
each  side  with  ganglionic  enlargements.  Follow  it  forward  to 
the  brachial  plexus,  —  then  across  this  plexus  and  on  the  side 
of  the  neck,  where  it  will  be  seen  to  lie  along  the  inner  side  of  a 
larger  nerve,  which  is  the  vagus.  Follow  it  to  the  head. 

Observe  carefully  the  branches  which  connect  each  sympa- 
thetic ganglion  with  a  spinal  nerve,  also  those  which  pass  off 
from  the  longitudinal  cord  and  the  ganglia  to  the  various  organs 
of  the  trunk.  Expose  the  whole  plexus  and  note  which  spinal 
nerves  it  is  made  up  of.  Find  the  nerves  which  go  to  the  shoul- 
der and  arm  and  follow  them  as  far  as  possible.  Note  the  rela- 
tion of  the  sympathetic  nerve  to  the  brachial  plexus. 

Exercise  15.  Draw  a  diagram  of  the  brachial  plexus  and  the 
nerves  proceeding  from  it,  and  the  anterior  portion  of  the 
sympathetic  system,  so  far  as  observed. 

Follow  the  longitudinal  sympathetic  nerve  posteriorly.  Ex- 
pose the  posterior  spinal  nerves  and  the  lumbo-sacral  plexus.  This 


148  VERTEBRATE  ZOOLOGY 

plexus  is  usually  made  up  of  the  last  six  spinal  nerves  of  the 
trunk  and  gives  rise  to  the  nerves  which  supply  the  hind  legs 
and  the  muscles  of  the  pelvis.  Follow  these  nerves  as  far  as 
possible. 

Exercise  16.  Draw  a  diagram  of  this  plexus  and  the  nerves 
springing  from  it,  and  the  posterior  portion  of  the  sympa- 
thetic system,  so  far  as  observed. 

The  special  sense  organs.  The  ear  contains  two  regions,  the 
inner  ear  or  membranous  labyrinth,  and  the  middle  ear  or  tympanic 
cavity,  —  the  former  being  the  essential  organ  of  hearing  which 
receives  the  auditory  nerves,  and  the  latter  the  space  bounded 
externally  by  the  tympanic  membrane. 

Carefully  disarticulate  and  remove  the  head,  taking  care  not 
to  cut  any  of  the  bones  of  the  skull  or  the  cervical  vertebrae. 

Remove  the  skin  which  covers  the  tympanic  membrane.  This 
will  be  done  easily  if  the  head  be  first  immersed  a  short 
time  in  hot  water.  Now  will  be  seen  the  circular  tympanic 
membrane,  —  a  thin  plate  of  cartilage  filling  the  external  opening 
of  the  tympanic  cavity.  With  a  sharp  scalpel  cut  the  tympanic 
membrane  around  its  edge  and,  lifting  it  up,  note  the  deli- 
cate, rodlike  columella,  which  will  be  seen  extending  inward 
from  it.  Snip  away  the  edges  of  the  tympanic  membrane  and 
finally  cut  it  from  the  columella,  exposing  the  cavity  of  the 
middle  ear. 

This  will  be  seen  to  be  a  large  space  which  extends  back 
from  the  opening  to  the  hinder  end  of  the  skull.  Probe  it.  The 
columella  extends  from  the  tympanic  membrane  to  a  point  on 
the  ventral  wall  of  the  cavity,  where  it  will  be  seen  entering  a 
long  canal  just  large  enough  to  contain  it ;  at  the  inner  end  of 
this  canal  the  columella  expands  and  is  applied  to  the  fenestra 
ovalis,  the  opening  into  the  inner  ear.  The  inner  end  of  the 
columella  and  the  fenestra  ovalis  will  not  be  seen.  Just  beneath 
the  columella  is  the  slitlike  inner  opening  of  the  Eustachian  tube ; 
probe  it  with  a  bristle  and  find  its  opening  into  the  pharynx. 

The  columella  is  a  bone  which  has  cartilaginous  ends.  Its 
function  is  to  conduct  the  sound  waves  to  the  inner  ear. 


A  TURTLE  149 

The  inner  ear,  or  membranous  labyrinth,  will  not  be  studied 
in  this  dissection. 

Exercise  17.  Draw   a    diagrammatic    sketch    of   the    tympanic 
cavity  on  a  large  scale. 

The  central  nervous  system  and  the  cranial  nerves  will  be 
studied  in  another  animal. 

The  skeletal  system.  This  system  of  organs  is  made  up  of 
two  portions,  —  the  exoskeleton,  which  is  dermal  in  origin,  and 
the  endoskeleton,  which  is  the  internal  bony  and  cartilaginous 
framework  of  the  body. 

The  exoskeleton  consists  of  the  horny  dermal  plates  (the  tor- 
toise shell)  and  scales  which  cover  the  external  surface  of  the 
body,  and  also  the  bony  dermal  plates  which  underlie  the  horny 
plates  and  help  form  the  shell.  The  bony  portion  of  the  shell 
is  not  composed  of  these  dermal  bones  alone  but  also  includes 
certain  portions  of  the  endoskeleton,  —  namely,  the  trunk  verte- 
brae, most  of  the  ribs,  and  perhaps  the  clavicle,  which  are  more 
or  less  completely  fused  with  the  dermal  bones.  The  exoskele- 
ton also  includes  the  claws  and  the  horny  covering  of  the  jaws. 

The  endoskeleton  is  made  up  of  the  axial  skeleton,  which  in- 
cludes the  skull  and  the  vertebral  column  and  ribs,  and  the 
appendicular  skeleton,  which  includes  the  framework  of  the  limbs 
and  the  girdles  by  means  of  which  they  are  firmly  attached  to 
the  trunk.  The  limbs  and  their  girdles  are  between  the  right 
and  left  rows  of  ribs  in  turtles ;  in  all  other  vertebrates  they  lie 
external  to  the  ribs. 

The  axial  skeleton.  Disarticulate  the  neck  and  remove  it 
with  the  head  from  the  carapace.  Disarticulate  and  remove  also 
the  pectoral  and  pelvic  girdles  with  the  legs,  and  the  tail. 

The  vertebral  column  contains  three  regions,  —  the  neck,  trunk, 
and  tail.  The  trunk  region  consists  of  the  vertebrae  and  the  ribs, 
which  enter  into  the  formation  of  the  carapace.  It  will  be  first 
studied. 

Boil  the  carapace  until  the  flesh  still  remaining  on  it  can  be 
easily  removed.  Care  must  be  taken  not  to  boil  it  so  long  that 
it  will  fall  to  pieces. 


150  VERTEBRATE  ZOOLOGY 

The  carapace.  Peel  off  the  horny  plates  and  note  that  they 
do  not  coincide  with  the  bony  plates  beneath.  Observe  the 
arrangement  of  the  bony  plates  as  seen  on  the  outer  surface. 
Note  which  of  these  plates  are  fused  with  the  trunk  vertebrae 
and  which  with  the  ribs. 

The  medial  row  of  plates  is  composed  of  the  single  anterior 
nuchal  plate,  followed  by  a  row  of  vertebral  plates  with  each  of 
which  is  fused  the  dorsal  portion  of  a  vertebra,  and  one  or  more 
posterior  pygal  plates.  At  each  side  of  the  median  row  is  a  row 
of  costal  plates,  with  which  the  ribs  are  fused,  and  lateral  to  them 
are  the  marginal  plates.  Certain  of  the  latter  plates,  in  most 
turtles,  extend  ventrally  and  meet  the  plastron. 

Exercise  18.  Make  an  outline  drawing  of  the  dorsal  surface  of 
the  bony  plates  of  the  carapace. 

Study  the  inner  surface  of  the  carapace.  Note  the  centra  of 
the  vertebrae  which  project  beneath  the  vertebral  plates  with 
which  they  are  fused.  Note  also  the  ribs  which  are  fused  with 
the  costal  plates.  Note  the  difference  between  the  first  pair 
of  ribs  and  those  following.  The  last  two  vertebrae  form  the 
sacrum,  which  supports  the  hinder  extremities. 

Exercise  19.  Draw  the  ventral  aspect  of  the  anterior  three  and 
also  of  the  posterior  two  vertebras  of  the  carapace,  with 
their  ribs  and  the  dermal  plates  with  which  they  are  fused. 

Separate  the  plates  of  the  carapace  from  one  another  and 
observe  carefully  the  difference  in  structure  between  the  first 
and  second  vertebras.  Note  the  articular  surfaces  on  the  first 
vertebra  with  which  the  posterior  cervical  vertebra  articulates. 
Study  also  the  costal  and  marginal  plates.  Note  the  sutures 
on  all  these  plates. 

The  plastron.  Peel  off  the  horny  plates.  Two  rows  of  bony 
plates  will  be  seen,  between  which  is  a  single  small  median 
plate.  The  anterior  pair  of  plates  are  called  the  epiplastrons,  and 
are  believed  to  be  homologous  with  the  clavicles  of  other  verte- 
brates. The  median  plate  is  the  entoplastron,  and  is  thought  to 
be  homologous  with  the  episternum.  The  two  middle  pairs  are 


A  TURTLE  151 

the  hyoplastrons  and  the  hypoplastrons,  and  the  posterior  pair  are 
the  xiphiplastrons. 

Exercise  20.  Draw  an  outline  of  the  plates  of  the  plastron. 

The  cervical  vertebrae.  Disarticulate  the  head  from  the  neck, 
being  careful  not  to  injure  the  hyoid  apparatus,  the  cartilagi- 
nous support  of  the  tongue  which  is  imbedded  in  the  muscles 
of  the  lower  jaw.  Thoroughly  clean  the  vertebrae  of  the  neck 
and  string  them  on  a  string  in  the  proper  order  so  as  not  to 
lose  the  sequence.  The  neck  contains  eight  vertebrae  which  are 
remarkable  for  the  variety  of  form  which  characterizes  them. 
They  fall  into  two  groups,  one  of  which  contains  the  first  and 
second  vertebrae ;  the  other  contains  the  remaining  six.  The 
first  two  vertebrae  form  the  support  of  the  skull.  The  first 
one  is  called  the  atlas.  It  is  a  ring-shaped  bone  which  is  made 
up  of  three  pieces,  —  two  dorsolateral  portions  representing  the 
neural  arch,  and  a  ventral  portion.  On  its  anterior  surface  is 
a  depression  in  which  the  condyle  of  the  skull  articulates.  The 
second  vertebra  is  called  the  axis.  It  is  made  up  of  a  cylin- 
drical centrum  and  a  neural  arch  through  which  the  spinal 
cord  runs.  At  the  anterior  end  of  the  neural  arch  is  a  pair  of 
articular  processes  —  the  prezygapophyses  —  and  at  its  posterior 
end  are  the  corresponding  postzygapophyses.  Short  transverse 
processes  and  no  ribs  are  present.  Projecting  forward  from 
the  anterior  end  of  the  centrum  is  the  odontoid  process.  It  lies 
within  the  arch  of  the  atlas,  the  centrum  of  which  it  represents. 

The  posterior  six  cervical  vertebrae  are  similar  to  the  axis, 
except  that  they  do  not  have  the  odontoid  process.  Study  each 
one  separately  and  note  the  points  in  which  they  differ  from  one 
another,  especially  in  the  form  of  the  end  surfaces  of  the  centra. 

Exercise  21.  Draw  on  a  scale  of  3  or  4  the  anterior  end  of  the 
atlas ;  a  side  view  of  the  axis  and  atlas ;  and  the  anterior 
end  of  the  fourth  vertebra. 

Study  the  caudal  vertebrae.  Note  the  rudimentary  ribs  on  the 
anterior  ones.  Are  the  centra  procoelous,  opisthocoelous,  or  am- 
phicoalous  ? 


152  VERTEBRATE  ZOOLOGY 

The  skull.  Disarticulate  the  lower  jaw  and  remove  it  together 
with  the  hyoid  apparatus,  being  careful  not  to  injure  the  latter. 
The  skull  is  made  up  of  two  regions,  the  cranium  and  the  visceral 
skeleton,  the  former  constituting  the  brain  case  together  with 
the  special  sense  capsules,  and  the  latter  being  made  up  of  the 
bones  and  cartilages  of  the  upper  jaw,  the  suspensorium  of  the 
lower  jaw,  the  lower  jaw,  and  the  hyoid  apparatus. 

We  shall  begin  with  the  study  of  the  lower  jaw  and  the 
hyoid  apparatus,  which  supports  the  tongue.  The  lower  jaw, 
or  mandible,  is  a  V-shaped  structure  composed  of  five  bones  and 
a  cartilage  on  each  side.  The  bones  are  very  firmly  knit  together, 
and  a  prolonged  boiling  may  be  necessary  to  make  the  sutures 
visible.  Before  this  is  done,  however,  observe  the  shape  of  the 
mandible,  the  cutting  edge  of  which  is  covered  by  horn,  the 
prominent  coronary  process  on  the  upper  surface  of  each  side, 
and  the  articular  surface  at  the  hinder  end  of  each  side.  Note 
also  on  the  inner  surface  of  each  side  a  long  groove  in  which 
lies  a  rod  of  cartilage.  This  is  Meckel's  cartilage. 

The  bones  in  the  mandible  are  the  following:  the  dentary, 
which  is  fused  with  its  fellow  of  the  opposite  side  and  forms 
the  front  part  of  the  jaw  and  most  of  the  outer  and  lower  sur- 
faces ;  the  coronoid,  which  forms  the  coronary  process  and  serves 
as  the  principal  surface  of  attachment  for  the  strong  jaw  muscles ; 
the  splenial,  which  forms  the  greater  part  of  the  inner  surface 
from  the  coronary  process  to  the  hinder  end ;  the  angular,  a  thin 
strip  beneath  the  splenial ;  the  supra-angular,  a  small  plate  above 
the  angular  at  the  hinder  end ;  and  the  articular,  which  forms 
the  greater  part  of  the  hinder  end.  The  last-named  bone  is  an 
ossification  in  the  hinder  end  of  Meckel's  cartilage ;  the  others 
are  all  membrane  bones. 

Exercise  22.  Draw  the  lower  jaw,  showing  the  outlines  of  these 
bones. 

The  hyoid  apparatus  consists  of  (a)  a  median  flattened  body, 
usually  a  cartilaginous  plate  the  dorsal  surface  of  which  is  con- 
cave and  holds  the  larynx,  and  (b)  two  pairs  of  lateral  projec- 
tions, or  cornua,  which  are  usually  partly  of  bone.  At  the  lateral 


A  TUKTLE  153 

border  of  the  anterior  portion  of  the  body  of  the  hyoid  on  each 
side  is  also,  in  many  turtles,  a  small  cartilaginous  projection. 

Exercise  23.  Draw  the  hyoid  apparatus. 

Thoroughly  clean  the  remainder  of  the  skull;  in  removing 
the  tympanic  membrane  note  the  columella,  a  minute  rod  of  bone 
which  extends  directly  inward  from  it.  Observe  the  general 
character  of  the  skull.  The  cranial  bones,  which  form  the  greater 
part  of  it,  and  the  visceral  bones,  which  form  the  upper  jaw  and 
a  part  of  the  roof  of  the  mouth,  are  firmly  joined  by  sutures 
and  together  form  a  very  strong  and  compact  whole. 

Observe  the  nostrils  or  anterior  nares  at  the  anterior  end,  and 
the  posterior  nares  in  the  roof  of  the  mouth;  also  the  circular 
orbits.  Note  at  the  hinder  end  of  the  skull  the  large  foramen 
magnum  and  the  long  bony  spine  projecting  above  it.  Note  that 
the  brain  cavity  is  much  narrower  than  the  whole  skull,  which 
is  very  wide  posteriorly,  and  that  an  extensive  arch  is  present 
on  each  side  just  back  of  the  orbit  which  partially  covers  a  space, 
—  the  temporal  fossa.  This  fossa  is  continuous  with  the  orbit 
in  front  and  extends  backward  as  a  wide  groove;  it  contains 
the  powerful  muscle  which  closes  the  lower  jaw.  Note  the  large 
external  ear  opening  and  the  position  of  the  tympanic  membrane. 
Note  the  condyle  by  which  the  skull  articulates  with  the  vertebral 
column ;  also  the  articular  surface  of  the  lower  jaw. 

Study  first  the  dorsal  surface  of  the  skull.  Beginning  at 
the  anterior  end,  the  medial  bones  are  the  paired  prefrontals, 
frontals,  and  parietals,  and  the  median  supraoccipital,  —  the  latter 
bone  bearing  the  long  spine  which  projects  back  from  the 
base  of  the  skull.  Identify  these  bones.  Lateral  to  the  medial 
bones  on  each  side  are  the  following  :  the  maxilla,  which  forms 
the  lower  and  the  anterior  borders  of  the  orbit;  the  postfrontal, 
which  adjoins  the  frontal  and  forms  the  upper  portion  of  the 
posterior  border  of  the  orbit ;  the  jugal,  which  is  just  ventral  to 
the  postfrontal  and  forms  the  lower  portion  of  the  posterior 
border  of  the  orbit ;  the  quadratojugal,  which  is  just  back  of  the 
jugal  and  forms  the  front  side  of  the  circular  opening  covered 
by  the  tympanic  membrane ;  the  squamosal,  a  large  bone  adjoining 


154  VEBTEBRATE   ZOOLOGY 

the  parietal,  which  forms  the  prominent  latero-posterior  end  of 
the  skull ;  the  quadrate,  which  forms  the  hinder  side  of  the  circu- 
lar tympanic  opening  and  terminates  below  in  the  articular  sur- 
face of  the  lower  jaw;  the  prootic,  a  small  bone  between  the 
quadrate  and  the  parietal,  which  is  pierced  by  the  foramen  of 
the  external  carotid  artery ;  the  opisthotic,  a  small  bone  directly 
back  of  the  prootic  and  between  the  squamosal  and  the  supraoc- 
cipital ;  the  epiotic,  a  small  bone  which  is  fused  with  the  lateral 
edge  of  the  supraoccipital  and  appears  as  a  part  of  it,  lying  in 
contact  with  the  opisthotic,  prootic,  and  parietal. 

Exercise  24.  Make  a  drawing  of  the  dorsal  aspect  of  the  skull  on 
a  large  scale,  showing  the  outlines  of  these  bones.  Care- 
fully label  all. 

Study  the  ventral  surface  of  the  skull.  The  bones  which 
appear  in  the  medial  area  are  the  following :  the  paired  premax- 
illae,  which  form  the  anterior  end ;  the  paired  maxillae,  which  are 
directly  back  of  the  premaxillse  and  with  them  support  the 
horny  biting  surface  of  the  jaws;  the  median  vomer,  a  slender 
bone  between  the  maxillae,  which  helps  form  the  walls  of  the 
posterior  nares ;  the  paired  palatines,  between  the  hinder  ends  of 
the  maxillae,  which  hold  the  vomer  between  them  and  help  form 
the  roof  of  the  mouth ;  the  paired  pterygoids,  large  bones  imme- 
diately back  of  the  palatines,  which  meet  each  other  in  the 
median  line  and  help  form  the  roof  of  the  mouth;  the  median 
basisphenoid,  immediately  back  of  the  pterygoids;  the  median 
basioccipital,  which  is  back  of  the  basisphenoid  and  forms  the 
hinder  end  of  the  skull.  Lateral  to  the  hinder  end  of  the 
pterygoid  on  each  side  is  the  quadrate,  back  of  which  is  the  squa- 
mosal ;  medial  to  the  hinder  part  of  the  last-named  bone  is  the 
opisthotic,  and  immediately  back  of  this,  the  exoccipital.  Note  that 
the  occipital  condyle  is  formed  of  three  portions,  and  determine 
the  bones  of  which  they  are  a  part. 

Exercise  25.  Make  a  drawing  of  the  ventral  aspect  of  the  skull 
on  a  large  scale,  showing  the  outlines  of  these  bones. 


A  TURTLE  155 

Cut  away  the  bony  arch  at  the  left  side  of  the  skull  and 
expose  the  temporal  fossa.  Identify  the  bones  which  have 
already  been  observed.  Along  the  ventral  margin  of  the  parie- 
tal note  the  small  alisphenoid  bone.  The  large  foramen  at  the 
inner  side  of  the  quadrate  is  for  the  passage  of  the  trigeminal 
nerve.  Note  that  the  two  orbits  communicate  with  each  other, 
not  being  separated  by  a  bony  septum ;  the  membranous  septum 
which  was  present  is  usually  destroyed  in  the  cleaning.  Note 
also  that  the  anterior  end  of  the  brain  case  is  not  bony. 

Exercise  26.  Make  a  drawing  on  a  large  scale  of  the  lateral 
aspect  of  the  skull. 

Study  the  posterior  aspect  of  the  skull.  Identify  the  bones 
and  other  features  already  mentioned.  At  the  side  of  the  con- 
dyle  are  two  foramina,  the  nearer  and  smaller  of  which  being 
that  of  the  hypoglossal  nerve  and  the  larger  that  of  the  vagus 
and  the  spinal  accessory  nerves. 

Exercise  27.  Make  a  drawing  on  a  large  scale  of  the  posterior 
aspect  of  the  skull. 

Of  the  bones  just  studied  the  following  belong  to  the  visceral 
skeleton,  forming  the  upper  jaw  and  the  suspensorium  of  the 
lower  jaw:  the  premaxillse,  maxillse,  jugals,  palatines,  ptery- 
goids,  quadratojugals,  quadrates,  and  squamosals,  —  of  which  the 
only  cartilage  bones  are  the  quadrates.  The  remaining  bones 
form  the  cranium ;  they  fall  into  two  categories,  —  those  of  the 
cranium  proper,  or  brain  case,  and  those  of  the  special  sense  capsules. 

The  bones  of  the  cranium  proper  fall  rather  easily  into  three 
groups :  a  posterior  group,  comprising  the  occipital  bones  ;  a 
middle  group,  comprising  the  basisphenoid,  the  alisphenoids, 
and  the  parietals ;  and  an  anterior  group,  comprising  the  frontal 
bones.  Of  these  the  occipital  bones  and  the  basisphenoid  are 
cartilage  bones,  the  others  being  membrane  bones.  The  presphe- 
noid,  orbitosphenoid,  and  ethmoid  elements  of  the  skull  remain 
cartilaginous  in  the  turtle  and  thus  will  not  appear  in  a  skull 
that  has  been  cleaned. 


156  VERTEBRATE  ZOOLOGY 

The  special  sense  capsules  are  the  auditory,  optic,  and  nasal. 
These  capsules,  which  are  entirely  cartilaginous  or  membranous 
in  the  embryo,  remain  largely  in  this  condition  throughout  the 
life  of  the  animal.  In  the  auditory  capsule  the  opisthotic,  prootic, 
and  epiotic  —  all  of  which  are  cartilage  bones  —  appear  on  each 
side,  the  epiotic  becoming  fused  with  the  supraoccipital.  The 
optic  capsule  is  entirely  membranous.  The  nasal  capsule  is  carti- 
laginous, the  only  bone  developing  in  it  being  the  vomer,  a 
membrane  bone.  Nasals  do  not  occur. 

Boil  the  skull  until  the  bones  can  be  separated  from  one 
another.  Take  them  apart  and  examine  each  carefully,  identi- 
fying the  bones  belonging  to  the  various  regions  of  the  skull. 

The  appendicular  skeleton  ;  the  anterior  extremities.  The  ante- 
rior extremities  are  composed  of  the  pectoral  girdle  and  the  fore 
limbs.  The  skeleton  of  the  former  is  made  up  of  three  bones  on 
.each  side  of  the  body, — a  cylindrical  dorsal  bone,  the  scapula,  and 
the  two  ventral  bones,  the  procoracoid  and  the  coracoid,  the  latter 
being  behind  the  former.  The  scapula  and  the  procoracoid  are 
continuous,  forming  a  single  piece ;  the  distal  ends  of  the  ventral 
bones  are  joined  by  a  ligament.  At  the  meeting  point  of  these 
three  bones  is  the  glenoid  fossa,  the  depression  in  which  the  humerus 
articulates. 

The  fore  leg  contains  three  divisions,  —  a  proximal,  a  middle, 
and  a  distal  division.  The  skeleton  of  the  proximal  division,  or 
upper  arm,  is  a  single  bone,  the  humerus.  That  of  the  middle 
division,  or  fore  arm,  contains  the  radius  and  the  ulna,  of  which 
the  former  is  preaxial  and  extends  farther  distally  than  the  latter. 
The  distal  division  is  the  wrist  and  hand.  The  skeleton  of  the 
wrist,  or  carpus,  is  made  up  of  nine  bones,  of  which  three  —  the 
ulnar,  intermedial,  and  radial  —  form  a  transverse  row  at  the  distal 
end  of  the  radius  and  ulna,  and  five,  which  are  called  the  carpals, 
form  a  row  at  the  proximal  end  of  the  hand.  The  first  carpal 
bone  abuts  on  the  radial.  Adjoining  the  ulnar  is  an  additional 
bone,  the  pisiform,  which  differs  from  the  others  in  that  it  is  a 
membrane  bone,  being  formed  as  an  ossification  in  a  tendon. 
It  is  thought  by  some  to  be  a  rudiment  of  a  sixth  finger  and  is 
homologous  to  a  similar  bone  in  mammals. 


A  TURTLE  157 

The  skeleton  of  the  hand  is  made  up  of  five  digits,  each  of 
which  is  composed  of  a  single  proximal  metacarpal  bone  and  sev- 
eral finger  joints  or  phalanges. 

Exercise  28.  Make  a  sketch  of  the  anterior  extremity,  showing 
accurately  the  outlines  of  all  these  bones. 

The  posterior  extremities.  These  are  composed  of  the  pelvic 
girdle  and  the  hind  limbs.  The  skeleton  of  the  former  is  composed 
of  three  bones  on  each  side,  the  dorsal  ilium,  and  the  ventral  pubis 
and  ischium,  the  former  of  which  is  in  front  of  the  latter.  At  the 
point  of  meeting  of  these  three  bones  is  the  acetabulum,  the  depres- 
sion in  which  the  femur  articulates.  The  dorsal  end  of  the  ilium 
articulates  with  the  sacrum.  The  two  pubic  bones  are  joined  in 
the  median  line  by  a  narrow  cartilaginous  plate.  The  two  ischial 
bones  are  smaller  than  the  pubes  and  contiguous  to  them,  and 
are  also  joined  by  a  median  cartilage. 

The  skeleton  of  the  hind  leg  is  made  up  of  three  divisions, — a 
proximal,  a  middle,  and  a  distal  division.  The  proximal  division, 
or  thigh,  is  composed  of  a  single  bone,  the  femur,  the  head  of 
which  fits  into  the  acetabulum.  The  middle  division,  or  shank, 
contains  two  bones,  the  tibia  and  fibula,  the  former  being  some- 
what larger  than  the  latter  and  preaxial  in  position.  The  distal 
division  is  composed  of  the  ankle  and  the  foot.  The  ankle  or 
tarsus  contains  six  small  bones  in  two  rows,  the  proximal  row 
consisting  of  the  smaller  fibular  and  the  larger  astragalus,  and  the 
distal  row  of  four  tarsal  bones,  of  which  the  largest  has  been  formed 
by  the  fusion  of  the  original  fourth  and  fifth  tarsals.  The  foot 
is  composed  of  five  digits,  each  of  which  contains  a  proximal 
metatarsal  bone  and  several  phalanges. 

Exercise  29.  Make  a  sketch  of  the  posterior  extremity,  showing 
accurately  the  outlines  of  all  these  bones. 

A  fresh  animal  will  be  needed  for  the  study  of  the  brain  and 
the  blood  vessels.  Kill  the  animal  and  remove  the  plastron,  as 
directed  on  page  136.  Very  carefully  chip  away  a  small  part  of 
the  wall  of  the  brain  case  so  as  to  admit  fluids  into  it.  The  brain 
can  be  studied  to  the  greatest  advantage  after  it  has  been  hardened 


158  VERTEBRATE   ZOOLOGY 

in  strong  alcohol  or  in  formalin.  We  shall,  consequently,  study 
the  blood  vessels  first  in  this  specimen  and  allow  the  brain  to 
be  hardening  while  they  are  being  dissected. 

The  vascular  system.  This  is  made  up  of  the  following 
organs :  (1)  the  heart ;  (2)  the  arteries,  the  vessels  through  which 
the  blood  is  carried  away  from  the  heart ;  (3)  the  veins,  the  ves- 
sels through  which  the  blood  returns  to  the  heart ;  and  (4)  the 
capillaries,  the  minute  vessels  connecting  the  veins  and  arteries. 

The  heart  and  the  great  veins  and  arteries  which  are  in  direct 
connection  with  it  have  already  been  studied.  We  shall  now 
make  a  detailed  study  of  the  veins,  and  after  them  of  the 
arteries.1 

The  veins  may  be  divided  into  two  groups :  (1)  the  systemic 
veins,  those  which  bring  venous  blood  from  the  various  organs 
and  tissues  to  the  sinus  venosus,  with  their  branches ;  and  (2)  the 
pulmonary  veins,  which  enter  the  left  auricle,  bringing  arterial 
blood  from  the  lungs. 

The  veins  of  the  first  group  may  be  further  subdivided  into 
(a)  the  caval  veins  and  their  branches,  which  bring  blood  directly 
to  the  sinus  venosus ;  and  (b)  the  portal  veins,  which  carry  it  first 
to  the  liver  and  kidneys. 

The  portal  veins.  Two  systems  of  portal  veins  are  present: 
the  hepatic  portal  veins,  by  which  blood  is  carried  from  the  stomach, 
intestine,  and  spleen  to  the  liver ;  and  the  renal  portal  veins,  which 
carry  the  blood  of  the  hind  quarters  to  the  kidneys.  Thes%  two 
systems  are  joined  by  the  two  abdominal  veins  which,  as  we  have 
already  seen,  lie  in  the  ventral  abdominal  wall  and  are  very 
conspicuous  when  the  plastron  is  removed. 

Follow  the  course  of  the  abdominal  veins  and  their  branches. 
At  a  point  opposite  the  heart  they  leave  the  peritoneum  and  pass 
dorsally  (inward)  to  the  liver ;  this  will  hardly  be  seen  at  present 
on  account  of  the  opacity  of  the  peritoneum.  At  the  angle  where 

1  Both  the  veins  and  the  arteries  can  he  studied  to  advantage  in  the  turtle  with- 
out being  injected ;  this  is  especially  true  of  the  veins,  which  are  colored  dark  by 
the  blood  which  remains  in  them  after  the  death  of  the  animal.  If  the  veins  are 
injected,  however,  it  must  be  done  at  several  places,  —  in  the  portal  or  one  of  the 
abdominal  veins  and  in  the  postcaval.  The  entire  arterial  system  is  easily 
injected  through  the  ventricle  of  the  heart. 


A  TURTLE  159 

this  turn  is  made  each  abdominal  vein  receives  an  anterior  vein 
from  the  pectoral  muscles.  With  forceps  pull  these  muscles 
loose  from  those  beneath  and  trace  the  further  course  of  this 
vein  and  its  branches.  It  will  be  seen  to  come  from  the  outer 
side  of  the  pectoral  girdle  and  to  receive  a  large  branch  from 
the  inner  side  of  this  girdle. 

Pressing  aside  or  removing,  if  necessary,  the  pelvic  muscles, 
study  the  distribution  of  the  posterior  branches  of  the  abdominal 
vein  and  the  renal  portal  system.  The  vein  will  be  seen  to  turn 
laterally  near  the  anterior  border  of  the  pelvis  and  to  pass  along 
or  just  beneath  this  border  toward  the  hind  leg.  Not  far  from 
the  turn  it  receives  a  branch  which  may  be  traced  backward  over 
the  pelvis,  near  the  hinder  border  of  which  it  is  joined  by  a 
vein  connecting  it  with  the  corresponding  vein  on  the  opposite 
side  of  the  body.  Trace  its  further  course. 

Return  now  to  the  main  vein  and  trace  it  to  the  muscles 
which  join  the  leg  with  the  inner  surface  of  the  carapace,  lift- 
ing up  the  pelvis  and  its  muscles  and  separating  them  from  the 
peritoneum  beneath.  Cut  the  skin  where  it  joins  the  carapace 
around  the  hinder  end  of  the  animal,  lift  it  up,  and  without  cut- 
ting anything,  separate  the  muscles  and  other  tissues  beneath  it, 
until  the  large  veins  are  seen.  The  abdominal  vein  may  be  in 
this  manner  traced  to  its  origin,  and  will  be  seen  to  be  formed 
by  the  union  of  three  large  veins,  —  the  femoral  vein  from  the  leg, 
the  caudal  vein  from  the  tail,  and  the  renal  portal  vein  which  passes 
dorsally  to  the  kidney.  Trace  the  renal  portal  vein  medially  to 
the  kidney,  and  the  other  two  veins  as  far  as  possible. 

With  sharp  scissors  cut  away  the  entire  ventral  portion  of 
the  peritoneum,  leaving,  however,  the  abdominal  veins  intact. 
Observe  the  anterior  ends  of  these  veins  where  they  pass  dor- 
sally and  enter  the  liver. 

Exercise  30.  Draw  a  diagram  showing  the  abdominal  veins  and 
their  anterior  and  posterior  branches  arid  the  renal  portal 
system,  so  far  as  observed. 

Study  the  hepatic  portal  system.  Cut  the  two  abdominal  veins. 
Raise  the  right  lobe  of  the  liver  and  examine  its  dorsal  surface. 


160  VEETEBEATE  ZOOLOGY 

Observe  the  gall  bladder  near  its  posterior  border  and  follow 
the  bile  duct  which  joins  it  with  the  intestine.  If  the  animal 
has  been  freshly  killed,  the  green  bile  may  be  squeezed  into  this 
duct  from  the  gall  bladder.  Lift  up  the  left  lobe  of  the  liver ; 
note  the  mesentery  which  joins  it  with  the  stomach,  and  the 
numerous  gastric  veins  which  run  from  the  wall  of  the  stomach 
to  the  liver.  Observe  again  the  pyloric  end  of  the  stomach  and 
the  whitish  pancreas  which  extends  from  it  along  the  intestine 
to  the  bile  duct. 

With  a  sharp  scalpel  or  scissors  cut  the  mesentery  just  men- 
tioned, freeing  the  liver  from  the  stomach  and  the  anterior  end 
of  the  intestine  as  far  back  as  the  bile  duct,  taking  care,  how- 
ever, not  to  cut  the  large  blood  vessels  near  it.  Turn  the  entire 
liver  forward  and  pin  it  there,  thus  exposing  its  dorsal  surface. 

Observe  the  large  and  conspicuous  branches  of  the  portal  vein 
which  run  across  the  dorsal  surface  of  the  liver,  partly  buried 
in  its  substance.  Find  the  point  where  the  branches  which 
traverse  the  two  main  liver  lobes  meet;  the  single  large  vein 
thus  formed  is  the  portal.  Trace  it  backward ;  it  will  be  found 
to  receive  a  number  of  veins,  of  which  the  largest  are  the  pan- 
creatic vein  from  the  pancreas,  and  the  mesenteric  vein  from  the 
mesentery.  The  latter  vein  is  formed  of  a  number  of  veins 
which  lie  in  the  mesentery  and  bring  blood  from  the  wall  of 
the  intestine.  Lift  up  the  intestine  and  trace  the  mesenteric 
vein  and  its  branches,  without,  however,  cutting  the  mesentery. 
Note  that  the  mesenteric  veins  are  accompanied  by  smaller  ves- 
sels,—  the  mesenteric  arteries.  Note  the  gastric  veins,  which  enter 
the  left  branch  of  the  portal  vein  from  the  wall  of  the  stomach. 

During  this  examination  the  spleen  will  be  seen  —  a  dark-red 
organ  the  size  of  a  pea  —  lying  in  the  mesentery  alongside  the 
intestine  and  near  the  point  where  the  mesenteric  vein  is  formed 
by  the  union  of  its  intestinal  branches.  The  postcaval  —  the 
largest  vein  in  the  body — will  also  be  seen  near  this  place,  and 
must  not  be  confused  with  the  veins  of  the  portal  system.  It 
comes  from  between  the  kidneys  in  the  hinder  part  of  the  body 
cavity,  passes  forward  close  to  the  spleen  and  the  right  lung, 
and  enters  the  right  lobe  of  the  liver. 


A  TUKTLE  161 

Joining  the  portal  vein  also  are  the  abdominal  veins,  which 
have  already  been  studied. 

Exercise  31.  Draw  a  diagram  of  the  hepatic  portal  system,  so 
far  as  observed. 

The  caval  veins.  Cut  the  intestine  back  of  the  bile  duct  and 
also  at  the  end  of  the  rectum,  and  remove  it  from  the  body. 
Bend  the  heart  forward  and  pin  it  there,  exposing  its  dorsal 
surface  and  the  base  of  the  large  caval  veins. 

Identify  the  ventricle,  the  two  auricles,  and  the  sinus  venosus. 
Four  large  veins  enter  the  sinus :  the  right  and  left  precaval  veins, 
bringing  blood  from  the  forward  part  of  the  body;  the  left  hepatic 
vein,  from  the  left  lobe  of  .the  liver;  and  the  postcaval  vein, 
which  brings  blood  from  the  hinder  part  of  the  body  and  the 
right  lobe  of  the  liver. 

Trace  the  left  precaval  vein ;  it  will  be  seen  to  be  formed  by 
the  union  of  two  veins,  —  the  subclavian  coming  from  the  fore  leg 
and  the  internal  jugular  from  the  side  of  the  neck.  Cut  the  skin 
between  the  forward  border  of  the  shell  and  the  shoulder,  find 
these  veins,  and  follow  them  as  far  as  possible. 

Trace  the  postcaval  vein.  We  have  already  seen  that  it  passes 
through  the  right  lobe  of  the  liver  and  receives  the  right  hepatic 
vein  not  far  from  the  heart.  It  may  now  be  followed  from  the 
hinder  border  of  this  right  lobe  to  a  middorsal  position  in  the 
abdominal  cavity,  where  it  lies  between  the  kidneys.  Here  it  is 
formed  by  the  union  of  a  number  of  renal  veins  from  the  kidneys 
and  genital  veins  from  the  genital  glands. 

Exercise  32.  Draw  a  diagram  representing  the  caval  veins  and 
their  branches,  so  far  as  observed. 

The  arteries.  Make  a  midventral  incision  in  the  skin  and 
expose  the  organs  of  the  neck.  Study  the  blood  vessels  which 
spring  from  the  anterior  side  of  the  ventricle,  carefully  dissect- 
ing them  free  from  the  tissues  surrounding  them.  Three  large 
arteries  will  be  seen,  side  by  side.  The  one  on  the  animal's 
right  is  the  innominate  artery ;  it  divides  at  once  into  the  right  and 
left  subclavian  arteries  which  go  to  the  fore  legs,  and  the  right  and 


162  VERTEBRATE  ZOOLOGY 

left  carotid  arteries  which  go  to  the  head.  In  the  angle  formed  by 
the  branching  of  these  arteries  lies  the  round  thyroid  gland.  Next 
to  the  innominate  artery  is  the  left  aorta,  which  springs  from  the 
right  side  of  the  ventricle  and  passes  to  the  left  side  of  the  body. 
Next  to  it  and  on  the  left  is  the  pulmonary  artery,  which  branches 
at  once  into  the  right  and  left  pulmonaries. 

After  these  arteries  have  been  dissected  free  from  the  sur- 
rounding tissues,  the  right  aorta  will  be  seen  beneath  the  innom- 
inate artery;  it  springs  from  the  left  side  of  the  ventricle  and 
passes  to  the  right  side  of  the  body;  the  right  and  left  pul- 
monaries will  also  be  seen.  The  right  and  left  aortas  meet  on 
the  dorsal  side  of  the  body  cavity  and  form  the  dorsal  aorta. 

Follow  these  arteries  and  their  main  branches,  beginning  with 
the  subclavian. 

The  subclavian  artery  gives  off  several  small  branches,  of  which 
one  passes  at  once  to  the  thyroid  gland,  one  runs  along  the 
ventral  side  and  one  along  the  dorsal  side  of  the  neck ;  it  then 
becomes  the  axillary  artery,  which  passes  above  the  brachial  nerve 
plexus,  and  finally,  as  the  brachial  artery,  goes  to  the  leg.  The 
axillary  artery  gives  off  a  branch,  the  internal  mammary,  which 
passes  to  the  outer  border  of  the  carapace  and  runs  backward 
along  it  to  the  hinder  part  of  the  body,  where  it  anastomoses 
with  the  epigastric  artery,  a  branch  of  the  dorsal  aorta. 

The  carotid  artery  is  smaller  than  the  subclavian,  and  may  be 
traced  forward  to  the  head.  In  the  greater  part  of  its  course  it 
lies  alongside  the  large  vagus  nerve,  the  much  smaller  sympa- 
thetic nerve,  and  the  internal  jugular  vein.  The  thymus  glands 
will  also  be  seen ;  they  are  a  pair  of  loose,  yellowish  masses  of 
tissue  at  the  base  of  the  neck. 

Follow,  now,  the  pulmonary  artery  and  the  aorta  on  the  left 
side  of  the  animal.  Push  the  stomach  and  left  lobe  of  the 
liver  to  the  animal's  right  and  trace  the  left  pulmonary  artery  to 
the  lung.  Note  again  the  left  pulmonary  vein,  and  trace  it  from 
the  lung  to  the  heart.  Trace  also  the  left  aorta  to  its  union  on 
the  dorsal  side  with  the  right  aorta.  It  gives  off  the  following 
large  arteries  :  the  coeliac  artery,  which  passes  to  the  wall  of  the 
stomach,  where  it  breaks  into  branches;  the  anterior  mesenteric 


A  TURTLE  163 

artery  which  supplies  almost  the  entire  intestine,  its  numerous 
branches  lying  alongside  those  of  the  mesenteric  vein ;  the  gas- 
troduodenal  artery,  which  divides  into  two  main  branches  and  sup- 
plies the  stomach,  duodenum,  and  pancreas.  Trace  all  of  these 
arteries  and  their  branches. 

In  young  animals  and  sometimes  in  adults  a  small  cross  artery 
will  be  seen  on  each  side,  which  unites  the  aorta  with  the  pul-  (/ 
monary  artery ;  it  is  called  the  ductus  Botalli. 

Follow  the  dorsal  aorta  now  to  the  hinder  end  of  the  body 
cavity,  where  it  passes  between  the  kidneys  alongside  the  post- 
caval  vein,  and  behind  them  divides  into  the  right  and  left  com- 
mon iliac  arteries.  A  number  of  small  arteries  will  be  seen  leaving 
the  dorsal  aorta,  one  of  which,  the  epigastric  artery,  passes  to  the 
lateral  border  of  the  carapace,  on  each  side,  where  it  runs  for- 
ward and  finally  anastomoses  with  the  internal  mammary  artery. 
Trace  these  small  arteries. 

Each  common  iliac  artery  divides  very  soon  into  the  internal 
and  the  external  iliacs.  The  former  gives  off  branches  which 
supply  the  colon,  rectum,  and  cloaca.  The  latter  gives  off 
branches  to  the  muscles  of  the  pelvis,  and  then,  as  the  sciatic 
artery,  supplies  the  leg.  Follow  the  sciatic  and  its  branches. 

Exercise  33.  Draw  a  diagram  of  the  arterial  system  so  far  as 
observed. 

Exercise  34.  Draw  a  diagram  of  the  entire  vascular  system. 

The  brain  and  the  cranial  nerves.  Cut  off  the  head.  With  a 
strong  scalpel  or  bone  forceps  cut  the  bone  from  the  dorsal  side 
of  the  cranium  and  also  partly  from  the  lateral  sides ;  carefully 
remove  the  dura  mater-4-  the  connective-tissue  membrane  cover- 
ing the  brain  —  and  study  its  dorsal  surface.  Its  anterior  divi- 
sion —  the  cerebrum  —  makes  up  more  than  half  the  brain  ;  it  is 
composed  of  the  two  hemispheres,  from  the  forward  end  of  which 
project  the  olfactory  lobes.  Between  the  posterior  ends  of  the 
hemispheres  is  the  delicate  pineal  body,  the  only  part  of  the  thala- 
mencephalon  —  the  second  division  of  the  brain  —  which  appears. 
Back  of  this  appear  the  paired  optic  lobes,  the  dorsal  portion  of 


164  VERTEBRATE   ZOOLOGY 

the  midbrain,  —  the  third  division.  Behind  the  optic  lobes  are 
the  cerebellum  and  the  medulla  oblongata,  —  the  fourth  and  fifth 
divisions.  Remove  the  vascular  choroid  plexus,  the  dark-colored 
membrane  which  forms  the  dorsal  surface  of  the  medulla,  when 
a  triangular  depression  —  the  fourth  ventricle  of  the  brain  — 
will  be  exposed. 

Exercise  35.  Draw  the  dorsal  aspect  of  the  brain  on  a  scale  of 
3  or  4. 

Remove  enough  of  the  side  of  the  cranium  to  expose  the  side 
of  the  brain.  Carefully  tilt  the  brain  to  one  side  and  study  the 
twelve  pairs  of  cranial  nerves.  The  first  pair — the  olfactory  nerves 
—  proceeds  from  the  olfactory  lobes  of  the  hemispheres  and 
goes  to  the  nasal  capsules.  The  second  pair — the  optic  nerves  — 
springs  from  the  ventral  surface  of  the  thalamencephalon  and 
proceeds  to  the  eyes.  The  third  and  fourth  nerves — the  oculo- 
motor and  the  trochlear — are  very  small  nerves  which  pass  from 
the  posterior  portion  of  the  midbrain  to  the  muscles  of  the  eye- 
balls, the  oculomotor  arising  from  the  ventral  and  the  trochlear 
from  'the  lateral  surface  of  the  midbrain. 

The  fifth  nerve — the  trigeminus — is  a  large  nerve  which  leaves 
the  side  of  the  anterior  end  of  the  medulla  oblongata ;  it  passes 
forward  and  soon  swells  to  form  the  Gasserian  ganglion,  which  lies 
on  the  inner  surface  of  the  skull  and  may  have  been  removed 
with  it.  From  this  ganglion  three  nerves  spring  and  pass  to  the 
outside  of  the  skull ;  these  are  the  ophthalmic,  which  passes  for- 
ward and  enters  the  orbit  just  back  of  the  optic  nerve;  the 
maxillary,  which  also  passes  forward  and  enters  the  orbit,  where 
it  divides  into  two  branches ;  and  the  mandibular,  which  passes 
out  through  the  same  foramen  with  the  superior  maxillary  and 
is  distributed  to  the  muscles  of  the  jaw. 

The  sixth  nerve  —  the  abducens  —  is  a  small  nerve  which  arises 
from  the  ventral  surface  of  the  medulla  near  its  anterior  end 
and  passes  to  the  muscles  of  the  eye.  The  seventh  and  eighth 
nerves  —  the  facial  and  auditory  —  spring  together  from  the  side 
of  the  medulla  back  of  the  trigeminus,  the  former  passing  to  the 
muscles  of  the  upper  jaw  and  the  latter  into  the  ear  capsule. 


A  TUKTLE  165 

The  ninth  nerve — the  glossopharyngeal — arises  from  the  side  of 
the  medulla  and  passes  to  the  muscles  of  the  tongue  and  phar- 
ynx. The  tenth  and  eleventh  nerves — the  vagus  or  pneumogastric 
and  the  spinal  accessory  —  arise  each  by  a  number  of  roots  from 
the  side  of  the  medulla  ;  the  former  passes  along  the  side  of  the 
neck  to  the  pharynx,  larynx,  lungs,  and  stomach ;  the  latter  goes 
to  the  muscles  of  the  neck  and  shoulder.  The  twelfth  nerve 
—  the  hypoglossal  —  arises  from  the  ventral  surface  of  the  me- 
dulla near  its  hinder  end  and  passes  to  the  muscles  of  the  tongue 
and  throat. 

Exercise  36.  Draw  the  lateral  aspect  of  the  brain  on  a  scale  of 
3  or  4,  and  show  the  origins  and  course  of  the  cranial 
nerves,  so  far  as  observed. 

Remove  enough  of  the  skull  so  that  the  brain  can  be  taken 
out.  Place  it  in  a  dish  of  alcohol  or  water  and  study  its  ven- 
tral surface.  Identify  the  hemispheres  and  the  olfactory  lobes.  On 
the  ventral  surface  of  the  thalamencephalon  is  the  optic  chiasma 
and  the  infundibulum,  —  the  latter  bearing  at  its  distal  end  the 
hypophysis.  The  ventral  portion  of  the  midbrain  is  formed  by 
the  crura  cerebri.  Behind  this  is  the  medulla  oblongata. 

Exercise  37.  Draw  the  ventral  aspect  of  the  brain  on  a  scale  of 
3  or  4. 


CHAPTER  IV 

BIRDS 
THE   PIGEON 

The  domestic  pigeon  is  one  of  the  best  birds  for  dissection 
because  of  its  convenient  size  and  the  ease  with  which  it  can 
usually  be  obtained.  All  birds  are,  however,  essentially  alike  in 
structure,  and  these  directions  may  be  used  with  the  chicken, 
the  sparrow,  or  any  other  common  bird. 

Two  specimens  will  be  needed  for  a  complete  dissection, — one 
for  the  study  of  the  outer  form  and  the  viscera,  and  one  for  the 
muscles  and  the  skeleton.  They  should  be  killed  as  needed  by 
being  placed  in  a  closed  jar  with  a  little  chloroform  or  ether, 
and  during  the  dissection  should  be  kept  in  a  one  per  cent  solu- 
tion of  formalin.  Care  should  always  be  taken  that  the  speci- 
mens be  covered  by  the  preserving  fluid,  otherwise  they  will 
mold ;  the  fluid  should  also  be  changed  as  often  as  it  becomes 
stale. 

Study  the  external  characters  of  the  animal.  The  most  dis- 
tinctive feature  of  a  bird  is  the  feathers,  which  clothe  almost 
the  entire  body  and  are  so  arranged  on  the  fore  limbs  and  tail 
as  to  enable  it  to  fly.  Feathers  are  highly  specialized  epidermal 
structures  and  are  allied  to  reptilian  scales ;  they  are  present  in 
all  birds,  and  in  no  other  animals.  Feathers  are  not  only  of 
great  importance  to  the  bird  in  enabling  it  to  fly,  but  they  are 
very  effective  in  checking  the  radiation  of  heat  from  its  body, 
as  they  form  a  warm  outer  covering.  It  is  largely  because  of 
the  development  of  feathers  that  birds  have  become  warm- 
blooded animals.  The  ordinary  temperature  of  a  bird's  body  is 
about  105°  Fahr.,  varying  a  few  degrees  in  different  species. 

Note  the  three  kinds  of  feathers,  —  the  contour  feathers,  down 
feathers,  and  pinfeathers.  The  contour  feathers  form  the  outer 

166 


THE  PIGEON  167 

surface  of  the  body  and  give  it  its  outline ;  note  their  method 
of  overlapping  and  the  smooth  surface  they  present  to  the  air. 
The  quills,  which  form  the  beating  surface  of  the  wings  and 
the  tail,  are  elongated  contour  feathers. 

The  down  feathers  are  soft  and  fluffy ;  they  clothe  the  nestlings 
and  are  also  found  between  the  contour  feathers  in  the  adult. 
The  pinfeathers,  or  filoplumes,  are  hairlike  structures  which  lie 
among  the  other  feathers  and  will  be  seen  when  they  are 
removed. 

Note  the  arrangement  of  the  feathers  on  the  body.  Observe 
first  those  parts  which  are  entirely  bare,  as  the  bill,  eyelids,  etc. 
The  greater  part  of  the  body  is  apparently  covered  by  the  con- 
tour feathers,  but  a  careful  examination  will  show  that  there 
are  distinct  feather  tracts  and  other  parts  which  have  no  feathers. 
These  tracts  can  be  distinguished  better  in  a  young  pigeon  or 
a  sparrow  than  in  an  adult  pigeon,  in  which  they  tend  to  run 
together.  It  will  be  seen  that  the  down  feathers  and  pinfeathers 
are  present  on  the  tracts  not  covered  by  contour  feathers. 

Besides  the  feathers,  other  epidermal  structures  are  present 
which  help  form  the  outer  covering  of  the  body ;  these  are  the 
horny  scales,  plates,  and  claws  on  the  legs  and  toes,  and  the 
horny  covering  of  the  beak. 

Observe  the  color  of  the  animal  and  determine  if  the  color 
tracts  are  bilaterally  symmetrical.  In  a  wild  state  the  color 
pattern  of  an  animal  has  a  strong  tendency  toward  bilateral 
symmetry,  but  domestication  changes  the  action  of  natural 
selection,  which  has  given  an  animal  its  peculiar  characters, 
and  often  results  in  the  confusion  of  the  color  patterns.  The 
coloration  of  the  European  rock  pigeon,  the  wild  ancestor  of  the 
domestic  pigeon,  is  similar  to  that  of  the  common  slate-colored 
domestic  pigeons. 

Observe  the  general  shape  of  the  body.  It  is  a  compact, 
rigid  structure,  a  laterally  compressed  ellipsoid  in  shape,  with 
a  long  neck  and  large  head,  large  wings,  feet,  and  tail.  The 
shape  fits  the  animal  to  be  propelled  rapidly  through  the  air. 
The  neck  of  a  bird  is  usually  very  flexible  because  the  trunk  is 
rigid,  —  a  correlation  we  found  also  in  the  case  of  the  turtle. 


168  VERTEBRATE  ZOOLOGY 

The  large  head  indicates  intelligence,  the  large  wings  and  tail 
a  powerful  flight,  and  the  strong  feet  ability  to  walk  well. 

The  body  may  be  divided  into  four  regions,  —  the  head,  neck, 
trunk,  and  tail. 

The  head.  This  body  division  articulates  with  the  vertebral 
column  by  a  single  condyle  and  consequently  has  great  range 
of  movement.  It  has  a  high,  arched  cranial  or  posterior  portion 
and  is  prolonged  anteriorly  to  form  the  conical  beak,  which  is 
made  up  of  the  upper  and  lower  jaws,  and  is  the  organ  of  pre- 
hension. Note  that  the  upper  jaw  possesses  considerable  flexi- 
bility and  is  not  so  rigidly  joined  with  the  cranium  as  is  the 
case  in  mammals  and  in  the  turtle.  The  mouth  is  large  and  is 
without  lips.  The  nostrils  or  external  nares  are  a  pair  of  slits 
near  the  base  of  the  upper  beak  and  just  in  front  of  a  swollen 
area  called  the  cere.  The  eyes  are  large  and  round  and  each  has 
three  lids,  an  upper  and  a  lower  lid,  —  both  movable,  the  latter 
more  so  than  the  former, — and  a  nictitating  membrane,  a  third  lid. 
This  membrane  is  situated  at  the  anterior  corner  of  the  eye, 
where  it  is  entirely  concealed  when  not  in  use,  and  moves  back 
and  forth.  With  fine  forceps  pull  it  over  the  eye.  The  open- 
ing of  the  ear  is  just  behind  the  eye  and  leads  to  the  tympanic 
cavity;  note  the  feathers  which  guard,  the  opening.  There  is 
no  external  ear. 

The  head  of  all  modern  birds  is  remarkable  in  that  it  contains 
no  teeth  and  no  strong  masticatory  muscles  ;  a  considerable 
weight  is  thus  spared  it.  This  is  a  feature  which  is  also  corre- 
lated with  the  great  powers  of  flight  which  most  birds  possess. 
Flying  is  one  of  the  most  difficult  and  highly  developed  methods 
of  locomotion  among  animals,  and  makes  necessary  a  careful 
adjustment  of  the  weights  to  be  carried:  It  is  very  much  to 
the  advantage  of  a  flying  vertebrate  that  the  heavier  portions 
of  the  body  be  brought  as  near  the  center  of  gravity  as  possible, 
and  that  the  various  organs  be  lightly  constructed. 

Thus  the  teeth,  which  are  composed  of  the  densest  and  one 
of  the  heaviest  tissues  of  the  body,  have  entirely  disappeared 
in  the  course  of  the  evolution  of  the  modern  bird.  But  a  grain- 
eating  bird  like  the  pigeon  must  chew  its  food,  because  only  in 


THE  PIGEON  169 

a  finely  reduced  condition  is  the  food  digested  quickly  enough 
to  furnish  the  needed  amount  of  heat  and  energy.  Instead, 
however,  of  the  chewing  being  done  in  the  mouth,  as  it  is  in 
the  mammals,  the  other  group  of  warm-blooded  vertebrates,  the 
performance  of  this  function  is  removed  to  the  gizzard,  a  part 
of  the  stomach,  which  is  situated  very  near  the  center  of 
gravity. 

Another  effect  which  has  been  correlated  with  the  loss  of 
teeth  in  the  bird  is  the  development  of  a  greater  intelligence. 
Inasmuch  as  the  weight  of  the  head  is  strictly  limited  by  the 
conditions  of  the  animal's  existence,  a  larger  brain  could  develop 
than  would  have  been  possible  if  the  teeth,  which  characterized 
primitive  birds,  had  not  disappeared. 

The  long  neck  is  loosely  inclosed  in  the  skin.  Near  the  base 
of  the  neck  is  the  crop,  an  expansion  of  the  oesophagus  for  the 
storage  of  food;  in  it  is  also  secreted  the  milklike  substance 
called  pigeon's  milk,  with  which  the  nestlings  are  fed. 

The  trunk  is  made  up  of  two  subregions,  —  the  thoracic  and  the 
abdominal  regions;  to  the  former  belong  the  wings,  to  the  latter 
the  legs,  by  means  of  which  the  bird  exercises  its  two  very 
different  methods  of  locomotion.  Both  of  these  subregions  are 
rigid  ones,  inasmuch  as  the  attachment  of  the  locomotory  or- 
gans to  the  trunk  must  be  firm  and  solid;  thus  the  whole  trunk 
is  a  firm,  boxlike  structure.  The  viscera  in  the  trunk  are  very 
compactly  arranged,  much  more  so  than  in  the  mammal,  and 
are  supported  in  the  troughlike  dorsal  surface  of  the  breast- 
bone. On  the  ventral  side  of  the  thoracic  region,  on  each  side 
of  the  breastbone, — the  keel  of  which  can  be  felt  in  the  median 
line, — are  the  great  pectoral  muscles,  the  principal  muscles,  of 
flight.  In  some  birds,  as  the  humming  bird,  these  muscles  con- 
stitute more  than  half  the  bulk  of  the  body ;  in  the  pigeon  they 
form  about  a  fourth. 

The  trunk  contains  the  air  sacs,  which  are  large,  thin-walled 
sacs  lying  among  the  other  viscera,  and  communicating  with 
the  bronchi  of  the  lungs  and  the  hollow  centers  of  many  of  the 
bones.  These  sacs  are  reservoirs  of  air ;  their  function  is  some- 
what obscure,  but  they  probably  help  supply  the  lungs  during 


170  VEBTEBKATE   ZOOLOGY 

rapid  flight  when  sufficient  air  could  not  be  inspired  through 
the  nostrils  to  supply  the  demands  of  the  system.  Place  a 
blowpipe  in  the  glottis,  at  the  root  of  the  tongue,  and  blow 
the  lungs  full  of  air;  it  will  be  seen  that  the  entire  trunk  swells 
out,  all  the  air  sacs  being  filled. 

The  anus  —  the  external  opening  of  the  cloaca  —  is  a  trans- 
verse slit  with  thickened  lips  on  the  ventral  surface  of  the  trunk 
near  the  base  of  the  tail ;  it  will  be  seen  when  the  feathers  are 
removed. 

The  tail  is  short  and  wide ;  it  has  received  the  name  of  the 
uropygium.  It  is  of  great  importance  to  the  animal,  as  its  long 
quills  help  to  support  it  in  the  air  and  to  direct  the  course 
of  its  flight.  There  are  twelve  of  these  tail  quills  in  common 
pigeons;  the  number,  however,  varies  in  the  different  breeds. 
Besides  these,  the  tail  also  bears  the  tail  coverts,  —  small  contour 
feathers  at  the  base  of  the  quills  on  both  the  dorsal  and  the 
ventral  surfaces.  The  tail  contains  the  uropygial  gland,  with  the 
secretion  of  which  the  bird  oils  its  feathers;  its  opening  is  on 
a  large  papilla  on  the  dorsal  surface  of  the  tail.  This  is  the 
only  skin  gland  in  the  body. 

The  appendages.  Two  pairs  are  present,  —  an  anterior  pair, 
the  wings,  and  a  posterior  pair,  the  legs.  The  wings,  which  are 
homologous  to  the  fore  legs  of  the  other  vertebrates,  offer  an  ex- 
tensive surface  to  the  air;  each  is  made  up  of  three  divisions, — 
the  proximal,  middle,  and  distal,  —  which  correspond  to  the  upper 
arm,  the  fore  arm,  and  the  wrist  and  hand.  The  hand  contains 
three  digits,  of  which  the  first  is  free,  the  second  and  third  being 
fused  together. 

The  upper  arm  is  short  and  partly  within  the  trunk,  and  usu- 
ally does  not  bear  wing  quills.  These  are  borne  by  the  forearm 
and  the  hand,  and  are  divided  into  two  groups,  —  the  primary 
quills  and  the  secondary  quills.  The  former  are  ten  in  number 
and  are  attached  to  the  hand;  the  latter  are  about  thirteen 
in  number  and  are  attached  to  the  forearm.  Besides  these,  a 
small  tuft  of  feathers,  which  is  independently  movable,  is  pres- 
ent on  the  outer,  forward  side  of  the  wing.  These  feathers  are 
attached  to  the  first  digit,  or  thumb,  and  form  what  is  called  the 


THE  PIGEON  171 

ala  spuria.    The  shorter  contour  feathers  on  both  dorsal  and  ventral 
surfaces  at  the  base  of  the  wing  quills  are  the  wing  coverts. 

The  legs  are  each  made  up  of  three  divisions,  —  the  proximal, 
middle,  and  distal,  —  which  correspond  to  the  thigh,  the  shank, 
and  the  ankle  and  foot  respectively.  The  thigh  is  within  the 
skin  of  the  trunk  and  does  not  project  beneath  it.  The  shank 
is  the  upper  end  of  the  drumstick  ;  it  is  a  stout,  muscular  struc- 
ture which  projects  from  the  trunk.  The  distal  division  of  the 
leg  is  composed  of  a  vertical  shaft  and  four  toes.  The  shaft  is 
the  lower  end  of  the  drumstick  and  is  formed  by  a  fusion 
of  the  tarsal  and  metatarsal  bones,  and  hence  is  equivalent  to 
the  ankle  and  foot.  The  toe  directed  backward  is  the  first ;  the 
second  toe  is  the  inner  one  of  the  three  directed  forward. 
Observe  the  arrangement  of  the  feathers  and  scales  upon  the 
leg  and  toes ;  observe  the  number  of  joints  in  each  toe. 

Exercise  1.  Draw  an  outline  of  a  side  view  of  the  animal  with 
the  wings  closed,  not  putting  in  the  separate  feathers. 
Label  all  the  parts  carefully. 

Exercise  2.  Draw  a  dorsal  view  of  the  head. 

Exercise  3.  Extend  one  of  the  wings  and  draw  its  dorsal  surface, 
showing  the  various  groups  of  feathers. 

Thoroughly  pick  the  pigeon.  This  is  done  much  more  easily 
and  quickly  if  the  bird  be  first  dipped  in  hot  water.  The  pick- 
ing had  better  be  done  in  an  opened  towel  to  prevent  the 
feathers  from  getting  scattered. 

Observe  carefully  the  delicacy  of  the  skin.  Note  the  filo- 
plumes,  or  pinfeathers.  Observe  also  the  shape  of  the  body,  the 
length  of  the  neck,  the  large  size  of  the  pectoral  muscles,  and 
the  form  of  the  tail.  Observe-  between  the  anterior  ends  of 
the  pectoral  muscles  the  V-shaped  depression  in  which  the  crop 
lies ;  on  each  side  of  it  one  arm  of  the  wishbone  may  be  felt. 
Find  the  pore  of  the  uropygial  gland,  and  squeeze  oil  out  of  it. 
Note  the  shape  of  the  anus  and  its  thick,  projecting  lips. 

Note  the  three  divisions  of  the  wing.  In  the  distal  division 
find  the  three  digits,  —  the  short,  movable  thumb  which  supports 


172  VEBTEBKATE  ZOOLOGY 

the  ala  spuria,  and  the  second  and  third  digits  which  are 
grown  together.  Note  the  alar  membrane,  which  lies  in  the  angle 
between  the  upper  arm  and  the  fore  arm.  Note  the  three  divi- 
sions of  the  leg.1 

The  mouth  and  pharynx.  Open  the  mouth  and  cut  through 
the  angle  of  the  jaw.  Carry  the  cut  back  through  the  muscles 
of  the  head  almost  to  the  opening  of  the  ear.  Disarticulate  the 
lower  jaw  and  turn  it  down,  exposing  the  cavity  of  the  mouth 
and  pharynx. 

There  will  be  seen  to  be  a  single  space  which  lies  between  the 
edges  of  the  bill  and  the  oesophagus,  that  part  of  it  within  the 
bill  being  the  mouth  cavity,  and  the  posterior  part,  the  pharynx. 
This  latter  space  is  where  the  course  of  the  respiratory  air  from 
the  nostrils  to  the  lungs  crosses  that  of  the  food  from  the  mouth 
to  the  stomach. 

Note  the  long  tongue,  and  its  shape.  Just  back  of  it  is  the 
glottis,  the  opening  into  the  larynx  and  the  windpipe ;  note  its 
shape  and  the  character  of  its  lips.  Back  of  the  glottis  is  a 
paired  transverse  membrane  with  fringed  edges,  projecting  from 
the  floor  of  the  pharynx,  behind  which  is  the  opening  of  the 
oesophagus.  Note  the  two  elongated  plates  which  form  the  roof 
of  the  mouth,  .also  the  serrated  medial  edges  of  their  hinder  por- 
tion. Note  the  elongated,  paired  posterior  nares,  through  which 
the  nasal  capsules  open  into  the  pharynx  ;  they  are  in  the  roof  of 
the  pharynx  opposite  the  glottis.  Just  behind  them  is  the  single 
median  opening  of  the  paired  Eustachian  passages,  which  join  the 
pharynx  with  the  tympanic  cavity ;  pass  a  bristle  through  it.  Note 
the  paired  folds  in  the  roof  of  the  pharynx  opposite  the  fringed 
ventral  folds,  all  of  which  guard  the  opening  into  the  ossophagus. 

Exercise  4.  Draw  a  sketch  of  these  structures  on  a  scale  of  2. 

1  If  it  is  intended  to  inject  the  blood  vessels,  it  must  be  done  now.  This  is 
best  performed  by  means  of  a  fine  cannula,  through  the  brachial  artery  and  the 
brachial  vein,  which  will  be  seen  on  the  inner  surface  of  the  wing,  the  vein 
being  the  larger  of  the  two.  The  femoral  artery  and  vein  may  also  be  easily 
injected ;  they  will  be  seen  in  the  leg  by  separating  the  muscles.  The  circulatory 
system  can,  however,  with  the  exception  of  the  smaller  vessels,  be  easily  studied 
without  the  aid  of  injection. 


THE  PIGEON  173 

The  internal  organs ;  the  air  sacs.  These  sacs  arise  from  the 
outer  surface  of  the  lungs  and  extend  as  thin-walled  pockets 
among  the  viscera  and  the  muscles,  and  beneath  the  skin ;  they 
also  extend  into  many  of  the  bones,  such  as  the  humerus,  femur, 
sternum,  and  others.  A  branch  of  a  bronchus  leads  directly  to 
each  sac. 

Insert  a  blowpipe  into  the  glottis  and  inflate  the  lungs  and 
the  air  sacs. 

There  are  several  important  sacs.  The  paired  abdominal  sacs  lie 
near  the  dorsal  wall  of  the  abdominal  cavity,  dorsal  to  the  intes- 
tine, coming  near  the  ventral  surface  posteriorly ;  they  join  the 
hinder  end  of  the  lungs.  The  paired  posterior  thoracic  sacs  lie  behind 
and  beneath  the  lungs  and  along  the  outer  sides  of  the  abdom- 
inal sacs;  they  join  the  sides  of  the  lungs.  The  anterior  thoracic 
sacs  lie  in  front  of  and  partly  beneath  the  posterior  thoracic  sacs  ; 
they  join  the  ventral  surface  of  the  lungs.  The  interclavicular  sac  is 
a  branched  structure  which  lies  beneath  the  anterior  end  of  the 
breastbone  and  the  clavicle ;  it  joins  each  lung  just  in  front  of  the 
main  bronchus ;  on  each  side  it  is  joined  by  an  axillary  sac  which 
lies  beneath  the  shoulder.  The  paired  cervical  sacs  lie  in  front  of 
the  lungs,  with  the  anterior  ends  of  which  they  communicate. 

It  is  impossible  to  dissect  out  these  sacs  without  destroying 
the  organs  among  which  they  lie.  Some  of  them,  however,  can 
easily  be  seen.  Lay  bare  the  humerus,  the  large  bone  in  the 
upper  arm,  and  cut  a  hole  in  it.  Insert  the  blowpipe  in  the 
glottis  or  in  a  slit  in  the  trachea,  and  blow  into  the  lungs. 
The  air  will  be  felt  coming  out  of  the  humerus,  which  is  a 
hollow  bone  containing  a  branch  of  the  axillary  sac. 

Make  a  mid  ventral  incision  through  the  abdominal  wall  from 
the  hinder  end  of  the  breastbone  to  the  anus ;  do  this  by  lift- 
ing up  the  wall  with  forceps  and  cutting  it  with  scissors:'  Make 
a  transverse  incision  on  each  side  along  the  hinder  end  of  the 
breastbone  and  cut  away  the  flaps  of  the  abdominal  wall.  Inflate 
the  lungs  again ;  the  abdominal  sacs  will  be  filled  and  brought 
into  view.  Note  the  great  delicacy  of  their  walls.  Under  the 
wings  will  be  seen  the  axillary  sacs,  and  beneath  the  crop,  the. 
interclavicular  sac, 


174  VEETEBEATE  ZOOLOGY 

The  viscera.  Lay  bare  the  breastbone,  removing  the  pec- 
toral muscles  from  it.  Cut  the  breastbone  loose  from  its  attach- 
ments along  its  posterior  and  lateral  margins.  Lift  it  up  gently 
and  observe  the  falciform  ligament, — a  transparent,  median  mesen- 
tery which  joins  it  with  the  organs  beneath.  Note  the  large  liver 
beneath  the  hinder  part  of  the  breastbone.  Cut  the  falciform 
ligament  and,  still  lifting  up  the  breastbone,  note  the  large 
heart  which  lies  in  its  concave  dorsal  surface.  Entirely  remove 
the  breastbone  from  the  body,  cutting  with  scissors  the  ribs  at 
its  side  and  the  bones  of  the  shoulder  girdle,  which  join  the 
breastbone  with  the  shoulder  blade.  Be  careful  to  avoid  cutting 
the  blood  vessels. 

Observe  the  organs  in  the  body  cavity,  but  without  disturb- 
ing them ;  note  the  compactness  with  which  they  are  placed. 
The  body  cavity  may  be  subdivided  into  two  spaces,  —  the  large 
abdominal  cavity,  which  is  lined  by  the  glistening  peritoneum  and 
contains  most  of  the  viscera,  and  the  pericardial  chamber,  which  is 
formed  by  the  pericardium  and  contains  only  the  heart. 

Observe  the  pericardium  surrounding  the  heart.  Back  of  it 
is  the  large  two-lobed  liver.  Beneath  and  back  of  the  left  lobe 
is  the  gizzard.  Covering  the  organs  back  of  the  liver  is  a  mem- 
brane filled  with  fat.  This  is  the  great  omentum,  —  the  mesentery 
of  the  stomach,  of  which  the  falciform  ligament  is  the  anterior 
portion.  Cut  around  the  border  of  the  great  omentum  and 
remove  it;  observe  the  coils  of  the  small  intestine,  which  fill 
the  hinder  part  of  the  cavity,  and  the  narrow  pancreas  which  lies 
between  two  of  its  folds. 

Exercise  5.  Draw  a  semidiagrammatic  sketch  of  the  opened  body 
cavity  within  an  outline  of  the  bird,  and  the  organs  as  they 
lie  in  it ;  carefully  label  all. 

The  digestive  system.  This  consists  of  the  mouth,  pharynx, 
oesophagus,  glandular  stomach,  gizzard,  small  intestine,  large 
intestine,  cloaca,  the  salivary  glands,  liver,  and  pancreas. 

Lift  up  the  liver  and  find  where  the  small  intestine  leaves 
the  gizzard,  in  the  middle  of  its  medial  surface.  The  anterior 
portion  of  the  small  intestine  forms  a  great  loop,  called  the 


THE  PIGEON  175 

duodenum,  within  the  bend  of  which  lies  the  pancreas.  Lift  up 
this  loop  and  note  its  extent.  Follow  the  intestine  to  its  hinder 
end  so  far  as  this  is  possible  without  cutting  any  of  the  organs 
except  the  walls  of  the  air  sacs.  Note  the  mesentery  of  the 
intestine  which  joins  its  coils  with  the  dorsal  body  wall ;  note 
also  the  large  veins  and  arteries  which  lie  in  it. 

Turn  the  liver  forward  and,  without  cutting  anything,  study 
its  dorsal  surface.  The  large  portal  vein  will  be  seen,  which 
enters  the  liver  near  the  median  plane  and  at  once  gives  off 
branches  to  its  lobes.  Near  this  point  are  the  two  bile  ducts 
which  carry  bile  from  the  liver  to  the  intestine.  Find  them. 
The  longer  duct  is  a  large  tube,  about  an  inch  in  length,  which 
runs  from  the  liver  to  the  right  limb  of  the  loop  of  the  duode- 
num. The  shorter  duct  is  also  large  and  enters  the  left  limb 
not  far  from  the  gizzard. 

Observe  the  shape  of  the  pancreas,  which  lies  in  the  duodenal 
loop.  Find  its  three  ducts ;  two  of  these  leave  the  pancreas 
near  its  middle  and  enter  the  right  limb  of  the  loop,  the  third 
duct  leaves  the  pancreas  in  front  of  the  other  two  and  passes 
forward  to  the  right  limb  of  the  loop. 

Exercise  6.  Draw  the  dorsal  aspect  of  the  liver,  showing  the 
branching  of  the  portal  vein,  the  two  bile  ducts,  the  duo- 
denum, and  the  pancreas  and  its  ducts. 

The  vascular  system.  This  is  made  up  of  the  following 
organs:  (1)  the  heart,  (2)  the  arteries,  (3)  the  veins,  (4)  the 
capillaries,  and  (5)  the  lymph  vessels.  The  heart  is  composed  of 
two  auricles  and  two  ventricles.  Two  systems  of  arteries  are 
present :  (a)  the  pulmonary  arteries,  which  take  venous  blood  from 
the  right  ventricle  to  the  lungs  to  be  aerated ;  and  (b)  the  systemic 
arteries,  which  take  arterial  blood  from  the  left  ventricle  to  the 
various  tissues  and  organs  of  the  body.  Two  systems  of  veins 
are  present :  (a)  the  pulmonary  veins,  which  bring  arterial  blood 
from  the  lungs  to  the  left  auricle ;  and  (b)  the  systemic  veins, 
which  bring  venous  blood  from  the  tissues  and  organs  of  the 
body  to  the  right  auricle. 


176  VEETEBEATE  ZOOLOGY 

The  systemic  veins  may  be  further  subdivided  into  two  sys- 
tems :  these  are  (a)  the  caval  veins,  —  those  veins  carrying  blood 
directly  to  the  heart,  and  their  branches ;  and  (b)  the  portal  systems 
of  veins,  which  carry  blood  from  certain  tissues  and  organs 
directly  to  the  liver  and  kidneys,  from  which  it  is  afterwards 
taken  to  the  heart  by  the  postcaval  vein. 

The  portal  veins.  Two  portal  systems  of  veins  are  present, — 
the  hepatic  portal  and  the  renal  portal  system. 

The  hepatic  portal  system.  We  have  already  seen  where  the 
hepatic  portal  vein  enters  the  liver.  This  vein  is  very  short, 
although  one  of  the  largest  in  the  body ;  it  will  be  seen  to  be 
formed  by  the  union  of  three  large  veins,  which  with  their 
branches  are  prominent  objects  in  the  intestinal  mesentery. 
These  are  the  gastroduodenal  vein,  which  comes  from  the  gizzard, 
the  duodenum,  and  the  small  intestine;  the  anterior  mesenteric 
vein,  which  comes  from  the  small  intestine  and  receives  numer- 
ous branches ;  and  the  posterior  mesenteric  vein,  which  lies  imme- 
diately dorsal  to  and  parallel  with  the  hinder  part  of  the 
small  intestine  and  the  rectum,  receiving  small  branches  from 
them. 

Without  cutting  the  mesentery  find  these  three  veins  and 
their  chief  branches.  The  first  two  are  easily  studied  by  turning 
over  the  various  loops  of  the  small  intestine.  In  order  to  see 
the  posterior  mesenteric,  press  forward  the  gizzard  and  the  entire 
small  intestine.  Note  also  in  this  connection  the  arteries  which 
lie  in  the  mesenteries  accompanying  the  branches  of  these 
mesenteric  veins. 

The  renal  portal  system.  Lying  against  the  dorsal  body  wall 
will  be  seen  the  large  red  kidneys,  one  on  each  side.  The  pos- 
terior mesenteric  vein  corresponds  to  the  abdominal  vein  of  reptiles 
and  amphibians,  although  it  differs  from  it  somewhat  in  posi- 
tion, and  joins  the  hepatic  with  the  renal  portal  system.  At  its 
inner  (dorsal)  end  this  vein  receives  the  small  caudal  vein  and  im- 
mediately divides  into  two  short  veins,  the  right  and  left  renal 
portals ;  each  of  these  goes  directly  into  the  hinder  end  of  one  of 
the  kidneys,  receiving  first,  however,  from  behind,  the  internal 
iliac  vein, 


THE  PIGEON  177 

The  dissection  of  these  veins  will  be  completed  when  the 
kidneys  are  studied. 

Exercise  7.  Draw  a  diagram  showing  the  portal  veins,  so  far  as 
observed. 

The  digestive  system  (continued).  Straighten  out  the  intestine 
by  cutting  its  mesentery;  leave,  however,  the  duodenal  loop 
uncut.  Separate  the  liver  and  gizzard  from  the  air  sacs  at  their 
left  and  turn  them  toward  the  animal's  right.  The  glandular 
stomach  will  be  brought  into  view ;  it  appears  as  a  forward  con- 
tinuation of  the  gizzard.  Trace  it  forward  to  the  oesophagus,  which 
enters  -it  just  dorsal  to  the  anterior  end  of  the  heart.  From  this 
point  the  oesophagus  runs  forward  to  the  pharynx ;  it  will  be 
studied  later  on. 

Study  the  divisions  of  the  digestive  tract  posterior  to  the 
oesophagus.  The  glandular  stomach  and  the  gizzard  are,  in  birds, 
equivalent  to  the  stomach  of  other  vertebrates ;  in  the  former, 
digestion  goes  on,  in  the  latter,  food  is  ground  up  and  prepared 
for  digestion.  The  walls  of  the  gizzard  are  very  thick  and  mus- 
cular and  its  cavity  is  lined  with  a  hard,  ridged,  cuticular 
membrane.  Note  the  round  red  spleen  by  the  glandular  stomach. 

The  intestine  begins  at  the  gizzard  and  is  divided  into  two 
portions,  the  small  intestine  and  the  large  intestine  or  rectum.  The 
small  intestine  is  very  long.  Its  anterior  portion  is  the  duodenum, 
which  forms  the  loop  inclosing  the  pancreas  and  receiving  the 
bile  and  pancreatic  ducts.  Its  posterior  portion  falls  into  two 
divisions  of  equal  length,  the  anterior  one  of  which  is  thicker  than 
the  posterior.  The  anterior  end  of  the  rectum  is  marked  by  a  pair 
of  small  sacs,  the  rectal  diverticula;  it  passes  to  the  cloaca, — a  short, 
wide  sac  which  opens  to  the  outside  through  the  anus  and  receives 
also  the  discharges  of  the  urinary  and  the  genital  organs. 

The  two  intestinal  glands  —  the  liver  and  pancreas  —  have 
already  been  studied. 

Exercise  8.  Draw  the  digestive  tract  so  far  as  observed. 

Cut  the  stomach  from  the  oesophagus  with  scissors ;  cut  the 
bile  and  pancreatic  ducts  and  free  the  stomach,  gizzard,  and 


178  VERTEBRATE  ZOOLOGY 

intestine  of  all  their  attachments  with  the  liver  and  other  organs, 
and  remove  them  from^he  body ;  do  not  disturb  the  liver. 

Cut  open  the  glandular  stomach  and  gizzard  and  the  duode- 
num and  observe  their  inner  surface.  Note  the  thick  walls  and 
the  hard  cuticular  lining  of  the  gizzard.  Observe  that  its  cavity 
can  be  tightly  closed  by  a  valve  and  shut  off  from  that  of  the 
glandular  stomach;  also  that  the  beginning  of  the  duodenum 
lies  close  to  the  hinder  end  of  the  glandular  stomach,  and  that 
when  the  gizzard  is  closed  fluids  would  pass  directly  from  the 
glandular  stomach  into  the  duodenum. 

Exercise  9.  Make  a  semidiagrammatic  drawing  of  the  opened 
glandular  stomach,  gizzard,  and  duodenum,  showing  these 
features. 

Cut  the  rectum  and  remove  the  digestive  tract  from  the 
body. 

The  urogenital  system.  The  urinary  system  consists  of  a  pair 
of  kidneys,  a  pair  of  ureters,  and  the  cloaca.  Each  kidney  is 
made  up  of  three  lobes,  which  lie  close  against  the  dorsal  body 
wall  in  the  posterior  part  of  the  body  cavity ;  the  peritoneum 
passes  over  their  ventral  surface.  Do  not  remove  them.  The 
ureters  are  a  pair  of  slender  tubes,  each  of  which  emerges  from 
the  hinder  border  of  the  anterior  lobe  of  the  kidney  and  passes 
along  the  ventral  surface  of  the  posterior  two  lobes,  straight 
back  to  the  dorsal  wall  of  the  cloaca,  receiving  branches  along 
its  course. 

Lying  on  the  ventral  surface  of  each  kidney  is  a  small  yellow- 
ish organ,  the  suprarenal  or  adrenal  body.  They  are  of  problemat- 
ical function,  but  do  not  belong  to  the  urogenital  system. 

The  genital  system  ;  the  male.  The  testes  are  a  pair  of  white, 
ovoid  bodies  which  lie  against  the  medial  borders  of  the  anterior 
lobes  of  the  kidneys.  Note  the  mesenterial  fold  which  attaches 
each  to  the  dorsal  body  wall.  They  are  joined  with  the  cloaca 
by  the  vasa  deferentia,  a  pair  of  convoluted,  slender  tubes  which 
pass  posteriorly  from  the  medial  border  of  the  testes  along  the 
ventral  surface  of  the  kidneys.  They  lie  lateral  to  the  ureters. 
The  hinder  end  of  each  is  dilated,  forming  a  vesicula  seminalis. 


THE  PIGEON  179 

The  female.  But  one  ovary  and  oviduct  are  present,  the  left 
ones;  those  on  the  right  side  are  present,  however,  in  the 
embryo.  The  ovary  is  a  granular  organ  which  lies  against  the 
medial  border  of  the  anterior  lobe  of  the  left  kidney,  attached  to 
it  by  a  mesenterial  fold ;  yellow  ova  of  various  sizes  will  usually 
be  seen  in  it.  The  oviduct  is  a  wide  tube  with  thin  walls  ante- 
riorly and  thick  walls  posteriorly,  which  extends,  suspended  in  a 
mesenterial  fold,  along  the  ventral  surface  of  the  left  kidney  and 
the  dorsal  body  wall  to  the  cloaca.  Its  anterior  end  opens  into 
the  body  cavity  by  a  much  elongated,  funnel-shaped  orifice  into 
which  the  ova  pass  when  they  escape  from  the  ovary.  A  rudi- 
ment of  the  right  oviduct  is  present  in  the  form  of  a  slender 
tube  extending  a  short  distance  forward  from  the  cloaca. 

The  oviduct  secretes  the  white  of  the  egg  and  the  shell,  as  the 
ovum  passes  down  it. 

The  absence  of  the  right  ovary  and  oviduct  is  an  additional 
feature  which  is  correlated  with  the  bird's  flight.  The  ovaries 
and  oviducts  are  both  bulky  organs  and  much  weight  is  saved 
by  the  elimination  of  those  on  the  right  side. 

The  cloaca  is  a  broad,  short  tube  which  opens  to  the  outside 
through  the  anus.  It  receives  the  rectum  at  its  forward  end ; 
the  two  ureters  and  the  genital  ducts  also  empty  into  it.  Cut  it 
open  by  a  slit  along  one  side,  wash  it  out,  and  study  its  interior. 
Find  the  openings  of  the  organs  just  mentioned,  and  note  their 
arrangement  with  reference  to  one  another.  Note  that  the 
rectum  opens  into  the  ventral  wall  of  the  cloaca  and  the  uro- 
genital  ducts  open  into  a  shallow  dorsal  pocket.  In  young 
birds,  and  occasionally  in  adults,  a  glandular  sac  called  the 
bursa  of  Fabricius  is  present  in  the  dorsal  wall ;  its  function  is 
unknown. 

Exercise  10.  Draw  the  urogenital  tract  and  the  cloaca. 

The  vascular  system  (continued] ;  the  heart.  Remove  care- 
fully the  delicate  pericardium.  The  heart  is  of  large  size  and 
conical  in  shape.  It  is  divided  into  four  chambers,  —  the  two 
auricles  and  the  two  ventricles.  The  auricles  form  the  anterior 
end  of  the  heart  and  are  marked  off  from  the  ventricles  by  a 


180  VEETEBBATE  ZOOLOGY 

line  of  fat.  On  the  surface  of  the  heart  are  seen  small  coronary 
veins  which  arise  in  the  heart  muscles  themselves. 

The  great  arteries.  Issuing  from  the  base  of  the  heart  between 
the  two  auricles  are  the  two  large  innominate  arteries  ;  they  together 
form  a  V,  between  the  arms  of  which  will  be  seen  the  trachea, 
or  windpipe.  Note  near  them  a  pair  of  slender  muscles  —  the 
tracheo-sternal  muscles  —  which  converge  to  the  ventral  surface  of 
the  trachea.  They  arise  on  the  inner  surface  of  the  sternum, 
which  has  been  removed  from  the  body ;  remove  these  muscles 
and  thoroughly  clean  the  arteries. 

The  innominate  arteries  do  not  arise  directly  from  the  heart, 
but  from  the  aorta.  This  large  vessel  springs  from  the  left 
ventricle,  and  at  once  giving  off  the  two  innominate  arteries 
continues  its  course,  first  dorsally  and  then  posteriorly,  as  the 
dorsal  aorta;  do' not  follow  it  at  present. 

Each  of  the  innominate  arteries,  after  a  course  of  about  a 
quarter  of  an  inch,  divides  into  two  vessels,  —  the  carotid  artery, 
which  runs  directly  forward  to  the  head,  and  the  subclavian  artery. 
This  latter  artery  is  very  short ;  it  gives  off  the  small  internal 
mammary  artery,  and  almost  at  once  divides  into  the  brachial 
artery,  which  runs  to  the  shoulder  and  supplies  the  wing,  and 
the  pectoral  artery,  which  supplies  the  pectoral  muscles. 

Follow  the  carotid  artery  forward.  Carefully  separate  the 
oesophagus,  with  the  crop,  from  the  organs  among  which  it  lies  ; 
note  the  large  blood  vessels  which  go  to  the  crop.  Note  the 
two  long  thymus  glands  which  lie  one  on  each  side  of  the  trachea 
along  almost  the  entire  length  of  the  neck ;  they  have  the  ap- 
pearance of  fat.  Lying  near  the  trachea  also  on  each  side  are  the 
cervical  artery,  the  large  jugular  vein,  and  the  vagus  nerve,  the  latter 
of  which  appears  as  a  white  cord ;  do  not  dissect  them  yet. 

The  carotid  artery  runs  just  beneath  the  jugular  vein  about 
half  an  inch,  and  then  gives  off  two  branches, — the  vertebral  artery, 
which  passes  medially  to  the  vertebrarterial  canal  of  the  cervical 
vertebrae  in  which  it  runs  to  the  brain,  and  the  cervical  artery, 
which  accompanies  the  vagus  and  the  jugular  vein  to  the  head. 

In  the  angle  between  the  carotid  and  the  cervical  arteries 
on  each  side  lies  the  small  thyroid  gland. 


THE  PIGEON  181 

The  main  trunks  of  the  two  carotids  now  converge  toward 
the  median  plane  and  pass  through  the  muscles  of  the  neck 
to  a  groove  in  the  ventral  surface  of  the  center  of  the  cervical 
vertebrae,  along  which  they  run  forward.  Near  the  head  they 
diverge,  and  each  passing  to  its  own  side  soon  divides  into  two 
arteries,  —  the  external  carotid,  which  supplies  the  outer  portions 
of  the  head,  and  the  internal  carotid,'  which  goes  to  the  brain. 

Study  the  subclavian  artery  and  its  branches.  One  of  the  latter, 
the  internal  mammary  artery,  passes  backward  along  the  inner 
surface  of  the  ribs.  Follow  the  brachial  and  pectoral  arteries,  and 
study  their  branching. 

Issuing  from  the  right  ventricle  is  the  pulmonary  artery ;  it 
divides  at  once  into  the  right  and  left  pulmonaries,  which  lie 
directly  dorsal  to  the  innominate  arteries  and  go  to  the  lungs. 

Exercise  11.  Draw  the  ventral  aspect  of  the  heart  and  the  ves- 
sels just  described. 

The  great  veins.  Turn  the  apex  of  the  heart  forward  and 
pin  it  there,  and  carefully  but  thoroughly  clean  its  dorsal  sur- 
face. Identify  the  right  and  left  auricles  and  the  right  and  left 
ventricles.  Three  large  veins  will  be  seen  entering  the  right 
auricle, — the  right  and  left  precaval  veins  and  the  postcaval  vein.  If 
these  are  not  seen  readily,  the  two  precavals  may  be  found  by 
following  the  large  jugular  veins,  one  of  which  is  on  each  side  of 
the  neck,  posteriorly.  The  right  precaval  is  a  very  short  vein  which 
enters  the  right  anterior  border  of  the  auricle.  It  is  formed  by  the 
union  of  three  large  veins,  which  meet  just  in  front  of  the  auricle, 
—  the  right  brachial  vein,  which  comes  from  the  wing;  the  right 
pectoral,  which  comes  from  the  pectoral  muscles ;  and  the  right 
jugular  vein,  which  comes  from  the  head.  The  pectoral  vein  re- 
ceives at  its  proximal  end  the  internal  mammary  vein,  which  lies 
alongside  the  mammary  artery  on  the  inner  surface  of  the  ribs. 

The  left  precaval  will  be  seen  passing  across  the  dorsal  surface 
of  the  heart  to  the  left  side  of  the  right  auricle ;  it  is  formed 
by  the  union  of  the  same  veins  as  the  right  precaval. 

Free  these  veins  from  the  tissues  surrounding  them.  Trace 
the  jugular  forward  along  the  side  of  the  neck,  where  it  lies 


182  VERTEBRATE  ZOOLOGY 

close  to  the  vagus  or  pneumogastric  nerve  and  the  cervical 
artery.  Beneath  the  under  surface  of  the  skull  the  two  jugulars 
are  united  by  a  transverse  vein.  Note  the  veins  from  the  thymus 
gland  and  the  crop  which  join  the  jugular,  and  note  also  the  large 
vertebral  vein.  This  vein  brings  blood  from  the  brain  and  lies  in 
the  vertebrarterial  canal  together  with  the  vertebral  artery. 

The  postcaval  vein  is  a  large  vessel  which  enters  the  right 
auricle  directly  from  behind.  It  brings  blood  from  the  hinder 
part  of  the  body  and  passes  through  the  right  lobe  of  the  liver 
to  the  heart ;  do  not  follow  it  posteriorly  at  present. 

Turn  the  heart  over  to  the  animal's  right  and  pin  it  there ; 
pull  the  heart  gently  forward  and  look  for  the  pulmonary  veins, 
which  bring  blood  from  the  lungs  to  the  left  auricle.  Each  is 
a  short,  wide  vein  which  will  be  seen  to  arise  from  the  lung  by 
several  roots  and  go  directly  to  the  left  auricle. 

Exercise  12.  Draw  the  dorsal  aspect  of  the  heart,  together  with 
the  precaval  and  pulmonary  veins  and  their  branches,  so 
far  as  these  have  been  observed. 

Follow  the  postcaval  vein  backward  through  the  right  lobe  of 
the  liver.  Note  the  hepatic  veins  which  enter  it  in  the  liver. 
Turn  the  right  lobe  over  to  the  animal's  left  and  note  where  the 
postcaval  vein  enters  it  from  behind.  Posterior  to  this  point 
and  near  the  anterior  end  of  the  kidneys,  the  postcaval  is  formed 
by  the  union  of  the  two  iliac  veins. 

Each  iliac  vein  is  formed  in  the  mass  of  the  anterior  lobe  of 
the  kidney  by  the  union  of  three  veins,  —  the  renal  portal,  the 
anterior  renal,  and  the  femoral  veins.  The  last  of  these  veins  comes 
from  the  leg  and  will  be  seen  approaching  from  the  side  and 
lying  between  the  first  and  second  lobes  of  the  kidney.  The 
renal  portal  has  already  been  mentioned.  It  enters  the  hinder 
lobe  of  the  kidney,  after  first  receiving  the  internal  iliac  vein  from 
behind,  and  passes  forward  imbedded  in  the  kidney,  giving  off 
numerous  small  branches.  It  thus  constitutes  a  portal  vein, 
inasmuch  as  it  distributes  blood  to  the  kidney  instead  of  send- 
ing it  directly  to  the  heart.  Instead  of  entirely  breaking  up, 
however,  into  small  veins  and  capillaries,  as  does  the  renal 


THE  PIGEON  183 

portal  of  the  lower  vertebrates,  it  soon  begins  to  increase  in 
size  and  joins  the  iliac.  Consequently  only  a  portion  of  the 
blood  brought  to  the  kidneys  by  the  renal  portal  veins  is  distrib- 
uted throughout  them ;  the  greater  part  probably  goes  directly 
to  the  iliacs  and  the  heart. 

The  anterior  renal  vein  is  a  large  longitudinal  vein  which 
appears  on  the  ventral  surface  of  the  kidney  near  the  median 
line,  imbedded  in  it. 

Carefully  follow  the  renal  portal  forward  by  picking  away 
the  substance  of  the  kidney  which  surrounds  it,  until  it  joins 
the  iliac  vein.  Follow  the  anterior  renal  and  the  femoral  veins 
to  the  iliac.  Follow  the  femoral  vein  into  the  leg  and  observe 
its  branching. 

Exercise  13.  Draw  a  semidiagrammatic  view  of  the  postcaval 
vein  and  its  branches,  together  with  an  outline  of  the 
organs  in  which  the  veins  lie. 

The  arteries.  Study  the  dorsal  aorta  and  its  branches.  Remove 
the  postcaval  vein.  The  dorsal  aorta  branches  off  from  the  right 
side  of  the  aorta  almost  immediately  after  that  vessel  leaves  the 
heart ;  it  forms  an  arch  over  the  right  side  of  the  heart  and  the 
right  bronchus,  and  reaches  a  dorsal  position  between  the  two 
lungs,  when  it  runs  backward  to  the  hinder  part  of  the  abdom- 
inal cavity.  Dissect  it  free  and  find  its  branches ;  cut  the  right 
bronchus  near  the  lung;  remove  the  thick  peritoneal  membrane 
which  covers  it. 

The  dorsal  aorta  gives  off  the  following  branches :  several  pairs 
of  small  costal  arteries,  the  coeliac,  anterior  mesenteric,  anterior 
renal,  femoral,  sciatic,  posterior  mesenteric,  internal  iliac,  and 
caudal  arteries. 

The  coeliac  artery  is  a  median  vessel  which  leaves  the  dorsal 
aorta  near  the  hinder  end  of  the  heart  and  runs  back  in  the 
mesentery,  sending  off  branches  to  the  stomach,  liver,  pancreas, 
gizzard,  and  anterior  part  of  the  intestine.  The  anterior  mesenteric 
is  a  large  median  artery  which  leaves  the  dorsal  aorta  a  short  dis- 
tance back  of  the  coeliac  artery  and  runs  back  in  the  mesentery, 
sending  branches  to  the  greater  part  of  the  intestine.  The 


184  VERTEBKATE  ZOOLOGY 

anterior  renal  arteries  are  a  pair  of  small  vessels  which  leave  the 
dorsal  aorta  opposite  the  anterior  lobes  of  the  kidneys  and  go  to 
them.  The  femoral  arteries  are  a  pair  of  vessels  which  leave  the 
dorsal  aorta  behind  the  anterior  renals  and  pass  above  the  kid- 
neys to  the  muscles  of  the  thigh. 

The  sciatic  arteries  are  a  pair  of  large  vessels  which  leave  the 
dorsal  aorta  opposite  the  middle  of  the  kidneys  and  pass  between 
their  middle  and  posterior  lobes  to  the  legs;  each  gives  off  a 
branch  to  the  middle  lobe  and  one  to  the  posterior  lobe  of  the 
kidney.  Follow  this  artery  into  the  leg.  The  median  posterior 
mesenteric  artery  and  the  paired  internal  iliac  arteries  leave  the  aorta 
together  near  the  hinder  end  of  the  kidneys,  the  former  going 
to  the  rectum  and  cloaca,  the  latter  to  the  muscles  of  the  pelvis. 
The  posterior  end  of  the  dorsal  aorta  is  the  caudal  artery,  which 
supplies  the  tail. 

Exercise  14.  Draw  a  semidiagrammatic  sketch  of  the  dorsal  aorta 
and  its  branches,  so  far  as  these  have  been  observed. 

The  internal  structure  of  the  heart.  Remove  the  heart  from 
the  body.  Identify  the  roots  of  the  three  caval  veins  which 
enter  the  right  auricle;  the  right  precaval  and  the  postcaval 
will  be  quickly  found ;  the  root  of  the  left  precaval  is  attached 
to  the  dorsal  wall  of  the  auricles  and  lies  across  them.  Identify 
the  roots  of  the  two  pulmonary  veins,  which  appear  near  together 
near  the  middle  of  the  dorsal  surface  and  enter  the  left  auricle. 
Identify  the  short  pulmonary  artery  and  its  right  and  left 
branches;  identify  the  aorta,  and  the  dorsal  aorta  together  with 
the  right  and  left  innominate  arteries  which  spring  from  it. 

Cut  across  the  wall  of  the  right  auricle ;  open  the  auricle,  and 
remove  the  blood  that  will  probably  be  found  caked  in  it.  Note 
the  openings  of  the  three  caval  veins ;  also  the  muscular  fold 
projecting  into  the  auricle,  which  forms  a  valve  guarding  the 
opening  of  the  postcaval.  Note  the  partition  separating  the 
right  from  the  left  auricle  ;  also  that  separating  the  right  auricle 
from  the  right  ventricle.  In  the  ventricle  is  a  deep  crescentic 
depression,  the  auriculo-ventricular  opening,  through  which  the 
blood  goes  into  the  ventricle. 


THE  PIGEON  185 

Make  a  median  longitudinal  slit  in  the  wall  of  the  right  ven- 
tricle and  note  the  small  extent  of  this  ventricle.  Note  the 
auriculo-ventricular  opening  and  the  valve  projecting  into  the  ven- 
tricle, which  prevents  the  flow  of  blood  back  into  the  auricle. 
Probe  through  the  pulmonary  arteries  into  the  right  ventricle ; 
follow  the  probe  with  scissors  and  cut  open  the  arteries.  Note 
the  three  transversely  placed  semilunar  valves  which  are  situated 
at  the  base  of  the  median  pulmonary  artery. 

Open  the  left  auricle  by  a  transverse  slit  through  its  wall  and 
remove  the  blood  in  it.  Note  that  the  pulmonary  veins  commu- 
nicate with  a  partly  separated  chamber  of  the  auricle.  Observe 
the  septum  separating  the  auricle  from  the  left  ventricle  and  the 
round  auriculo-ventricular  opening  in  it.  Open  the  left  ventricle 
by  a  median  longitudinal  slit;  note  the  thick  walls,  except  at 
the  apex,  and  the  relatively  small  cavity  with  its  longitudinal 
muscular  ridges.  The  auriculo-ventricular  or  mitral  valve  will  be 
seen  to  be  formed  of  two  flaps  which  are  joined  with  the  wall 
of  the  ventricle  by  cords,  the  chordae  tendinae.  Probe  the  aorta 
into  the  left  ventricle  and  follow  the  probe  with  the  scissors. 
Cut  open  the  aorta  and  note  the  three  pocketlike  semilunar  valves 
which  extend  across  its  base. 

Make  a  cross  section  of  the  heart  in  the  middle  of  the  two 
ventricles  and  note  the  shape  of  them  and  the  relative  thickness 
of  their  walls. 

Exercise  15.  Draw  a  diagram  showing  the  structure  of  the  heart. 
Exercise  16.  Draw  a  diagram  of  the  entire  vascular  system. 

The  respiratory  system.  This  consists  of  the  two  lungs  and 
the  air  sacs  in  connection  with  them,  the  two  bronchi  and  the 
trachea  by  which  the  lungs  are  placed  in  communication  with 
the  outside  world. 

The  lungs  are  spongy  bodies  lying  close  against  the  dorsal 
body  wall  and  are  covered  ventrally  by  the  pleura,  which  is  a 
tough,  thickened  portion  of  the  peritoneum.  The  lungs  are 
relatively  small  in  size  and  are  held  firmly  in  place  between  the 
pleura  and  the  dorsal  body  wall,  so  that  they  are  capable  of  very 


186  VERTEBBATE   ZOOLOGY 

little  movement.  They  are  not  saclike,  as  in  the  lower  land  ver- 
tebrates, but  spongy  as  in  mammals,  their  interior  being  entirely 
filled  with  air  cells.  They  are  joined  with  the  heart  by  the  pul- 
monary veins  and  arteries,  —  the  latter  carrying  venous  blood 
away  from  them  and  the  former  arterial  blood  to  them. 

Entirely  free  the  ventral  surface  of  the  lungs  from  the  blood 
vessels  and  other  structures  which  may  still  be  attached  to  them, 
but  do  not  injure  the  bronchi;  dissect  the  pleura  from  both 
lungs,  and  the  lungs  away  from  the  body  wall.  Note  their  inti- 
mate relation  to  this  wall.  Look  for  the  openings  into  the 
air  sacs. 

Separate  the  oesophagus  and  crop  from  their  attachments  with 
the  trachea  and  bronchi  and  turn  them  forward.  Note  the 
cartilaginous  rings  in  the  trachea  and  bronchi. 

Exercise  17.  Draw  a  sketch  of  the  lungs  and  the  trachea  and 
bronchi. 

The  bird  has  two  larynges,  i.e.,  two  regions  in  its  respiratory 
system  where  the  passage  of  air  into  and  out  of  the  lungs  is 
controlled  by  a  special  mechanism.  One  of  these  is  at  the 
anterior  end  of  the  trachea  and  is  homologous  to  the  larynx 
of  other  vertebrates;  the  other  is  at  its  posterior  end  and  is  called 
the  syrinx.  It  is  this  latter  organ  which  produces  the  voice  of 
the  bird. 

Study  the  structure  of  the  syrinx.  It  consists  of  a  chamber 
called  the  tympanum  at  the  hinder  end  of  the  trachea  which  is 
formed  at  this  place  by  the  coalescence  of  the  posterior  tracheal 
and  the  anterior  bronchial  rings;  in  this  chamber  is  a  vibrating 
membrane  called  the  semilunar  membrane  which  produces  the  voice. 
On  each  lateral  side  of  the  trachea  is  the  slender  broncho-tracheal 
muscle. 

Exercise  18.  Draw  the  ventral  aspect  of  the  hinder  end  of  the 
trachea  and  the  forward  ends  of  the  bronchi,  showing 
accurately  the  shape  of  the  rings,  on  a  scale  of  3. 

The  semilunar  membrane  is  a  delicate  median,  vertical  projection 
extending  into  the  tympanum  from  the  meeting  point  of  the 


THE  PIGEON  187 

medial  walls  of  the  bronchi.  It  is  stiffened  by  a  slender  cartilage 
called  the  pessulus  which  lies  in  a  dorsoventral  position. 

A  number  of  small  muscles  are  present  on  the  trachea  and  the 
bronchi,  which  play  a  part  in  the  production  of  the  voice.  These 
fall  into  two  groups,  —  those  which  join  the  trachea  with  neigh- 
boring bones,  and  those  which  are  confined  to  the  trachea  and 
bronchi.  These  muscles  vary  much  in  different  birds.  In  the 
pigeon  the  largest  are  the  tracheo-sternal  muscles,  —  a  V-shaped  pair 
which  join  the  trachea  with  the  sternum  and  were  seen  when 
the  great  arteries  issuing  from  the  heart  were  studied,  —  and 
the  broncho-tracheal  muscles,  the  lateral  pair  which  were  seen  on  the 
sides  of  the  trachea. 

Open  the  tympanum  by  a  lateral  slit  in  the  trachea  and 
bronchus  and  note  the  semilunar  membrane. 

Exercise  19.  Draw  a  semidiagrammatic  sketch  of  the  tympanum, 
showing  the  semilunar  membrane. 

Study  the  structure  of  the  larynx.  Dissect  the  anterior  end 
of  the  trachea,  with  the  larynx  and  tongue,  from  the  body.  The 
larynx  is  at  the  anterior  end  of  the  trachea;  its  opening  into 
the  pharynx  is  the  glottis.  Note  the  two  long  horns  of  the  hyoid 
bone  which  lie  on  either  side  of  the  glottis.  The  opening  of  the 
glottis  is  bounded  and  supported  on  either  side  by  the  .paired 
and  partly  ossified  arytenoid  cartilages.  Remove  the  delicate  mus- 
cles and  the  mucous  membrane  from  the  larynx  and  note  the 
shape  of  the  arytenoids. 

Back  of  these  cartilages  are  the  procricoid  and  cricoid  cartilages, 
which  are  modified  tracheal  rings.  A  thyroid  cartilage  is  not 
present  in  birds.  The  cricoid  cartilage,  which  is  often  wrongly 
called  the  thyroid,  is  a  partly  ossified  ring,  which  is  wide  ven- 
trally  and  incomplete  on  the  dorsal  side.  Between  its  dorsal 
ends  lies  a  small  median  plate,  the  procricoid,  sometimes  wrongly 
called  the  cricoid.  The  dorsal  ends  of  the  two  arytenoids  articu- 
late with  the  procricoid ;  the  ventral  ends  are  free. 

Exercise  20.  Draw  a  lateral  view  of  the  larynx  on  a  scale  of  2  or  3. 
Exercise  21.  Draw  an  outline  of  the  oesophagus  with  the  crop. 


188  VERTEBRATE  ZOOLOGY 

The  nervous  system.  This  consists  of  (1)  the  central  nervous 
system,  which  is  made  up  of  the  brain  and  the  spinal  cord;  (2)  the 
peripheral  nervous  system,  which  includes  the  paired  cranial  and 
spinal  nerves  and  the  sympathetic  nervous  system ;  and  (3)  the 
special  sense  organs. 

We  shall  first  study  the  spinal  nerves  and  the  sympathetic  nerv- 
ous system.  Remove  what  remains  of  the  kidneys  from  the  body, 
but  be  careful  not  to  injure  the  nerves  which  lie  beneath  them. 

The  spinal  nerves  are  those  which  place  the  spinal  cord  in  com- 
munication with  the  muscles  and  skin  of  the  trunk,  neck,  and 
limbs.  They  join  the  spinal  cord  in  pairs,  a  pair  lying  between 
each  two  vertebrae  in  the  intervertebral  foramina.  A  single 
spinal  nerve  is  formed  of  two  roots,  —  a  dorsal  root,  the  fibers  of 
which  are  sensory  in  function,  and  a  ventral  root,  which  is  motor ; 
on  the  former  is  a  large  swelling,  the  spinal  ganglion.  The  two 
roots  meet  outside  the  intervertebral  foramen,  at  the  distal  end 
of  the  ganglion. 

Observe  the  spinal  nerves  of  the  trunk ;  they  will  be  seen 
to  be  white  cords  lying  on  the  dorsal  wall  of  the  body  cavity 
between  and  parallel  with  the  ribs.  At  the  point  where  the 
neck  joins  the  trunk,  note  the  prominent  retractor  muscles,  which 
connect  the  ventral  and  lateral  surfaces  of  the  former  with 
the  ventral  surface  of  the  thoracic  vertebrae.  Cut  away  these 
muscles ;  lying  on  them  will  be  seen  on  each  side  a  white  cord,  the 
vagus  nerve.  Lying  opposite  to  these  muscles  at  the  base  of  the 
neck  will  be  seen  four  very  large  spinal  nerves  which,  together 
with  a  delicate  branch  from  the  next  nerve  back  of  them,  form 
a  network  called  the  brachial  plexus.  From  this  plexus  proceed  the 
nerves  which  supply  the  wing  and  the  muscles  of  the  breast. 

Thoroughly  clean  the  plexus  and  follow  the  nerves  which  go 
to  the  wing.  Note  the  spinal  ganglion  at  the  base  of  each  nerve. 
The  brachial  plexus  is  formed  of  the  eleventh  to  the  fifteenth 
spinal  nerves  inclusive. 

Exercise  22.  Draw  a  diagrammatic  view  of  the  brachial  plexus, 
showing  accurately  the  arrangement  of  the  nerves  as 
observed. 


THE  PIGEON  189 

The  five  spinal  nerves  following  this  plexus  proceed  straight 
laterally  to  the  muscles  of  the  trunk.  The  next  two,  which  are 
the  twenty-first  and  twenty-second,  form  the  lumbar  plexus ;  from 
it  nerves  go  to  the  muscles  of  the  thigh.  The  following  four 
nerves,  which  are  the  twenty-third  to  the  twenty-sixth  inclu- 
sive, form  the  sacral  plexus,  from  which  the  great  sciatic  nerve  pro- 
ceeds to  the  leg.  These  two  plexuses  are  joined  by  a  cross 
nerve.  Thoroughly  clean  these  nerves  and  follow  the  great 
sciatic  nerve  into  the  leg ;  observe  its  branching  throughout  the 
leg.  Posterior  to  the  sciatic  plexus  is  the  plexus  pudendus,  a  sim- 
ple union  of  the  seven  spinal  nerves  which  extend  obliquely 
back  to  the  tail. 

Exercise  23.  Draw  a  diagram  of  these  three  plexuses  and  the 
nerves  proceeding  from  them,  so  far  as  observed. 

Study  the  spinal  nerves  of  the  neck  in  front  of  the  brachial 
plexus.  Ten  pairs  are  present,  of  which  all  but  the  first  two 
pairs  may  be  seen  issuing  from  among  the  muscles  on  the  ven- 
tral side  of  the  neck  and  passing  dorsally. 

The  sympathetic  nervous  system  consists  of  a  pair  of  longitudinal 
nerve  cords  with  paired  ganglia  which  lie  on  either  side  of  the 
spinal  column  between  the  head  and  the  tail,  in  close  connection 
with  the  spinal  nerves.  The  cord  is  doubled  on  each  side  in 
the  trunk,  where  it  sends  off  numerous  branches  to  the  organs 
of  the  digestive  and  circulatory  systems. 

Find  the  main  sympathetic  nerves  of  the  trunk.  In  the 
anterior  and  middle  portions  of  the  trunk  the  main  nerve  cords 
lie  in  the  abdominal  cavity  along  the  base  of  the  ribs.  They 
consist  here  of  two  longitudinal  nerves  on  each  side  which 
meet  in  the  spinal  ganglia,  the  sympathetic  ganglia  and  the 
spinal  ganglia  being  fused.  Note  carefully  the  relation  of  these 
two  nerves  to  the  ribs.  At  the  base  of  the  brachial  plexus  are 
two  unusually  large  ganglia. 

Follow  the  nerves  and  the  ganglia  into  the  posterior  portion 
of  the  abdominal  cavity.  The  ganglia  will  be  seen  to  become 
rapidly  smaller,  and  in  the  caudal  region  they  are  wanting.  The 
double  sympathetic  nerve  extends  between  the  brachial  and  the 


190  VERTEBRATE  ZOOLOGY 

lumbar  plexuses,  posterior  to  which  a  single  strand  is  present  on 
each  side  of  the  spinal  column. 

A  network  of  nerves  starting  from  the  longitudinal  sym- 
pathetic nerves  and  ganglia  in  the  anterior  portion  of  the  body 
cavity  is  present,  from  which  the  large  splanchnic  nerve  springs. 
This  nerve  passes  medially  and  joins  the  solar  plexus,  a  network 
of  nerves  and  ganglia  surrounding  the  dorsal  aorta  and  the  base 
of  the  coeliac  and  anterior  mesenteric  arteries. 

In  the  cervical  region  the  sympathetic  system  consists  of  a 
single  longitudinal  nerve  on  each  side,  which  lies  in  the  verte- 
brarterial  canal  of  the  cervical  vertebrae,  together  with  the  ver- 
tebral artery  and  the  vertebral  vein.  It  will  not  be  seen. 

Exercise  24.  Draw  a  diagram  of  the  sympathetic  system,  so  far 
as  observed. 

The  special  sense  organs ;  the  olfactory  organ.  Entirely  remove 
the  skin  and  muscles  from  the  head ;  remove  also  the  eyelids, 
but  do  not  injure  the  eyeballs.  The  nasal  capsules  consist  of  a 
pair  of  cavities,  just  in  front  of  the  eyes,  separated  from  each 
other  by  the  median  septum  nasi.  They  are  in  communication 
with  the  outside  by  the  nostrils  or  anterior  nares,  and  with  the 
pharynx  by  the  posterior  nares. 

Remove  the  outer  wall  of  the  right  capsule  completely  and 
observe  the  interior.  Note  the  slitlike  posterior  nares.  In  the 
interior  are  three  swellings,  the  turbinals,  which  are  lateral  pro- 
jections of  the  septum  nasi.  Of  these,  the  two  anterior  are 
prominent,  elongated  structures  ;  the  third  lies  behind  and  some- 
what above  the  middle  turbinal  at  the  hinder  end  of  the  nasal 
cavity.  It  is  much  smaller  than  the  others,  and  the  only  one  to 
which  the  olfactory  nerve  goes. 

Exercise  25.  Draw  the  nasal  cavity. 

The  eye.  Note  the  large  size  of  the  eye.  Observe  the  front 
aspect  of  it.  The  outer  layer  is  the  cornea,  which  is  transpar- 
ent. It  is  a  continuation  of  the  black  sclerotic,  which  is  the  outer 
layer  of  the  back  part  of  the  eye ;  note  the  bony  ring  in  this 
layer.  Through  the  transparent  cornea  the  iris  and  pupil  will 


THE  PIGEON  191 

be  seen ;  the  former  is  a  yellow  ring,  the  latter,  the  round 
opening  into  the  interior  of  the  eye.  Lining  the  inner  surface 
of  the  eyelids  and  forming  the  outer  surface  of  the  cornea  is 
a  transparent  membrane  called  the  conjunctiva. 

Exercise  26.  Draw  these  features. 

The  muscles  of  the  eyeball.  Cut  away  the  bony  ridge  which 
surrounds  the  right  eye  and  thoroughly  expose  the  orbit,  but 
without  disturbing  the  eyeball  or  its  muscles,  or  cutting  through 
the  thin  skull  into  the  brain.  By  pressing  the  eyeball  back- 
ward, the  insertions  of  two  muscles,  the  superior  oblique  and  the 
inferior  oblique,  are  brought  into  view,  —  that  of  the  former  being 
on  the  medial  surface  of  the  eye  and  that  of  the  latter  on  the 
an tero- ventral  surface.  Both  muscles  have  their  origins  on  the 
anterior  wall  of  the  orbit.  Beneath  the  inferior  oblique  and 
between  it  and  the  wall  of  the  orbit  will  be  found  the  Harderian 
lachrymal  gland,  —  a  small,  fatlike  body  which  moistens  the  nicti- 
tating membrane.  The  lachrymal  gland  is  a  very  small  white  body 
at  the  hinder  side  of  the  eye,  and  may  not  be  seen. 

Just  back  of  the  insertion  of  the  superior  oblique  is  that  of 
the  superior  rectus  muscle.  Pull  the  eye  forward ;  the  insertion 
of  the  external  rectus  will  be  seen  on  the  posterior  side  of  the 
eyeball.  Cut  the  superior  oblique  at  its  insertion  and  pull  the 
eye  backward ;  beneath  it  will  be  seen  the  insertion  of  the  inter- 
nal rectus  muscle.  Cut  all  of  these  muscles  at  their  insertions  and 
pull  the  eyeball  backward  ;  the  inferior  rectus  will  be  seen,  which 
has  its  insertion  on  the  inner  surface  of  the  eye.  All  of  these 
rectus  muscles  have  their  origins  in  the  posterior  wall  of  the 
orbit. 

Lift  up  the  eyeball  and  cut  the  inferior  rectus  muscle  and 
the  optic  nerve ;  remove  it  from  the  orbit.  Without  disturbing 
any  of  the  structures  of  the  orbit,  observe  the  origins  of  the 
two  oblique  muscles  in  the  anterior  part  of  the  orbit,  and  of  the 
rectus  muscles  near  the  optic  nerve.  Lift  up  the  inferior  oblique 
and  find  the  Harderian  gland. 

Two  additional  muscles  are  present  which  control  the  nictitat- 
ing membrane, — the  quadrate  and  the  pyramidal  muscles.  These 


192  VEETEBEATE   ZOOLOGY 

lie  close  to  the  inner  surface  of  the  eyeball.  The  quadrate  is  a 
broad  muscle  the  origin  of  which  extends  from  the  dorsal  mar- 
gin of  the  eyeball  to  the  optic  nerve.  The  pyramidal  is  a  narrow 
triangular  muscle  which  extends  from  the  ventral  margin  to  the 
optic  nerve,  where  it  meets  the  inner  border  of  the  quadrate. 

Study  the  eye  itself.  The  outer  coating  is  the  sclerotic  layer, 
as  we  have  already  seen.  Cut  a  small  piece  from  the  side  of  the 
eyeball  near  the  bony  ring  which  surrounds  the  cornea :  the  two 
other  coatings  of  the  eye  —  the  choroid  layer  and  the  retina  —  will 
be  seen.  The  former  is  the  vascular  layer ;  it  contains  the  blood 
vessels  which  supply  the  eye ;  it  also  contains  the  pigment.  The 
iris  is  the  continuation  of  the  choroid  layer  over  the  front  of 
the  eye ;  in  it  are  circular  and  radial  muscle  fibers  by  the  action 
of  which  the  size  of  the  pupil  and  the  amount  of  light  which 
enters  the  eye  are  controlled. 

The  retina  is  the  soft  inner  coating  of  the  eye.  It  is  the 
essential  sensory  portion  of  it  and  the  direct  continuation  of 
the  optic  nerve.  Projecting  through  the  retina  at  the  back  of 
the  eye  is  a  prominent  pigmented  and  vascular  ridged  plate 
called  the  pecten.  It  belongs  to  the  choroid  layer  and  extends 
into  the  middle  of  the  eye  toward  the  lens,  with  which  it  is  joined 
by  a  transparent  ligament.  Its  function  is  unknown,  although 
it  may  be  to  supply  the  lens  with  nutriment.  It  may  be  easily 
observed  if  a  small  piece  be  cut  from  the  side  of  the  eyeball 
opposite  the  first  opening  made. 

Just  back  of  the  pupil  and  the  iris  is  the  crystalline  lens.  It  is 
lenticular  in  shape  and  flatter  on  the  outer  than  on  the  inner  side. 
It  is  held  in  position  by  the  ciliary  process,  to  which  it  is  attached 
by  a  delicate  circular  ligament ;  these  structures  lie  just  behind 
the  iris  on  the  inner  surface  of  the  bony  ring  which  surrounds 
the  cornea.  Cut  the  eyeball  in  two  by  an  equatorial  incision 
and  observe  the  inner  surface.  The  ciliary  process  will  be  seen 
surrounding  the  lens  and  may  be  distinguished  by  its  radiating 
fibers.  The  ciliary  muscles  are  also  present  in  the  ciliary  process  ; 
these  muscles  by  their  contraction  slightly  change  the  shape 
and  position  of  the  lens  and  thus  enable  it  to  focus  light  from 
objects  at  varying  distances  upon  the  retina. 


THE  PIGEON  193 

Scrape  away  the  ciliary  process  and  note  the  bony  ring  sur- 
rounding the  cornea;  it  is  composed  of  a  number  of  separate 
plates. 

The  interior  of  the  eye  is  divided  by  the  iris  and  the  lens  into 
two  cavities, — an  outer  one  between  the  cornea  and  the  iris  which 
contains  the  watery  aqueous  humor,  and  an  inner  one  between  the 
lens  and  the  retina  which  contains  the  jellylike  vitreous  humor. 

Exercise  27.  Draw  a  diagram  showing  the  structure  of  the  eye, 
so  far  as  observed. 

The  ear.  The  ear  consists  of  the  inner  ear  or  membranous 
labyrinth,  the  middle  ear  or  tympanic  cavity,  and  the  external 
auditory  meatus,  the  passage  leading  from  the  middle  ear  to  the 
outside.  The  inner  ear  is  the  essential  organ  of  hearing  to 
which  the  auditory  nerve  goes ;  the  middle  ear  is  joined  with  the 
pharynx  by  the  Eustachian  tube  and  is  separated  from  the  external 
auditory  meatus  by  the  tympanic  membrane  or  eardrum. 

Remove  the  lower  jaw.  Note  back  of  the  eye  the  external 
opening  of  the  meatus.  Cut  away  its  sides  on  the  right  side 
of  the  head  until  the  tympanic  membrane,  which  lies  at  the 
inner  end  of  the  meatus,  is  exposed.  This  membrane  is  circular 
in  shape  and  semitransparent.  On  its  inner  side  it  is  joined 
with  the  columella,  a  rod  of  cartilage  and  bone  which  extends 
across  the  tympanic  cavity  from  the  tympanic  membrane  to  the 
inner  ear.  Cut  around  the  edge  of  this  membrane,  lift  up  an 
edge,  and  the  columella  will  be  seen  within.  At  its  inner  end 
is  an  oval  bone  called  the  stapes,  which  covers  an  opening  in  the 
wall  of  the  inner  ear  called  the  fenestra  ovalis.  The  columella 
and  stapes  perform  the  same  function  as  the  three  ear  ossicles 
in  the  mammalian  tympanic  cavity;  they  convey  the  sound 
waves  from  the  tympanic  membrane  to  the  inner  ear. 

The  tympanic  cavity  and  Eustachian  tube  are  homologous  to 
the  first  visceral  cleft  of  fishes,  which  in  the  dogfish  forms  the 
spiracle. 

The  inner  ear.  The  principal  organs  of  the  inner  ear  which 
can  be  seen  in  a  dissection  are  the  three  semicircular  canals ;  care- 
fully shave  away  the  bone  in  the  auditory  region  and  expose 


194  VERTEBRATE   ZOOLOGY 

them.  Two  of  these  canals  are  vertical  in  position,  the  anterior 
being  the  larger  and  more  dorsal;  the  third  canal  has  a  hori- 
zontal position  and  lies  lateral  to  the  other  two.  These  canals 
spring  from  a  small  sac  called  the  utriculus,  just  beneath  which 
is  another  small  sac,  the  sacculus;  projecting  from  the  latter  is 
the  lagena,  which  corresponds  to  the  cochlea  of  mammals. 

Exercise  28.  Draw  a  diagram  showing  the  structures  of  the  ear 
which  have  been  observed. 

The  brain  and  the  cranial  nerves.  Entirely  remove  the  remain- 
ing skin  and  the  muscles  from  the  head  and  anterior  end  of  the 
neck;  remove  the  left  eye.  Beginning  at  its  hinder  side,  cut 
away  with  scalpel  and  scissors  the  roof  of  the  skull,  exposing 
the  dorsal  surface  of  the  brain.  The  skull  is  easily  cut  with  a 
scalpel  because  of  its  spongy  nature.  It  is  very  thin  and  the 
brain  entirely  fills  the  cavity ;  care  must  be  taken,  consequently, 
not  to  cut  too  deeply.  Cut  away  also  the  upper  half  of  the 
orbit  and  the  side  of  the  skull  behind  it. 

The  brain  is  made  up  of  five  divisions,  of  which  two,  the 
cerebrum  and  the  cerebellum,  project  prominently  dorsally  and 
form  almost  its  whole  dorsal  surface.  The  anterior  division  is 
the  cerebrum,  which  is  composed  of  the  two  large  hemispheres ;  at 
their  anterior  ends  are  the  two  small  olfactory  lobes.  Immediately 
behind  the  hemispheres  and  between  them  and  the  cerebel- 
lum is  the  delicate  pineal  body  or  epiphysis,  which  is  a  projec- 
tion of  the  dorsal  wall  of  the  second  division  of  the  brain,  — 
the  thalamencephalon. 

The  third  division,  or  midbrain,  is  composed  dorsally  of  the 
optic  lobes,  which  appear  as  a  pair  of  spherical  bodies  at  the 
sides  of  the  brain  between  the  ventral  portions  of  the  cerebrum 
and  the  cerebellum.  This  latter  division  is  the  fourth ;  it  is 
marked  by  transverse  grooves  ;  posteriorly  it  overlaps  the  medulla 
oblongata,  the  fifth  division,  which  is  continuous  with  the  spinal 
cord.  At  about  the  point  where  the  spinal  cord  passes  into  the 
brain,  the  former  turns  sharply  ventrally. 

Exercise  29.  Draw  a  view  of  the  dorsal  aspect  of  the  brain. 


THE  PIGEON  195 

Study  the  lateral  aspect  of  the  brain  and  the  twelve  pairs  of 
cranial  nerves,  so  far  as  these  can  be  dissected.  Entirely  remove 
one  side  of  the  cranium,  but  preserve  the  ventral  portion  of  the 
orbit,  with  the  large  nerves  which  cross  it.  The  first  pair  of 
cranial  nerves,  the  olfactories,  are  slender  prolongations  of  the 
olfactory  lobes  ;  they  pass  to  the  nasal  capsules.  The  second  pair, 
the  optic  nerves,  emerge  from  the  optic  chiasma  on  the  ventral  side 
of  the  second  division  of  the  brain  and  pass  to  the  orbits.  In 
order  to  see  them,  separate  the  floor  of  the  cranial  cavity  from 
the  cerebrum,  beginning  at  its  anterior  end.  The  whole  anterior 
end  of  the  skull  can  be  pressed  down  away  from  the  brain  so  as 
to  expose  the  ventral  surface  of  the  cerebrum  and  the  optic 
nerves.  The  optic  tracts  will  also  be  laid  bare.  They  will  be  seen 
immediately  back  of  the  optic  chiasma  on  each  side  and  abut- 
ting on  the  optic  lobes.  The  third  nerve,  the  oculomotor,  is  a 
small  nerve  which  arises  just  behind  the  infundibulum  on  each 
side  and  goes  to  the  orbit. 

The  fourth  nerve,  the  trochlear  or  pathetic,  will  be  seen  arising 
between  the  optic  lobe  and  the  cerebellum  on  the  side  of  the 
brain  and  passing  forward  to  the  orbit.  The  fifth  nerve,  the 
trigeminal,  is  a  large  nerve  which  arises  on  the  side  of  the  medulla 
just  beneath  the  optic  lobe  and  passes  forward  to  the  large  Gas- 
serian  ganglion.  This  structure  lies  in  a  depression  in  the  wall  of 
the  skull  and  gives  off  three  branches :  (1)  the  ophthalmic  nerve, 
which  runs  through  the  floor  of  the  skull  into  the  orbit;  it 
passes  along  the  upper  portion  of  the  orbit  to  a  foramen  in 
its  anterior  wall,  where  it  enters  the  nasal  capsule,  through  the 
entire  length  of  which  it  runs ;  (2)  the  maxillary  nerve,  which 
enters  the  orbit  and  passes  along  its  floor  to  the  upper  mandible ; 
(3)  the  mandibular  nerve,  the  largest  of  the  three,  which  enters 
the  orbit  and  divides  into  two  branches,  one  of  which  supplies 
the  temporal  muscle  while  the  other  runs  forward  to  the  lower 
mandible. 

The  sixth  nerve,  the  abducens,  is  short  and  small.  It  arises  on 
the  ventral  surface  of  the  medulla  near  the  median  line,  nearly 
opposite  the  base  of  the  trigeminal  nerve,  and  passes  through 
the  floor  of  the  skull  to  the  orbit.  It  will  be  seen  when  the 


196  VERTEBRATE  ZOOLOGY 

ventral  surface  of  the  brain  is  studied.  The  seventh  nerve,  the 
facial,  arises  just  back  of  the  trigeminal  on  the  lateral  side  of 
the  medulla,  and  runs  backward  in  two  branches  to  the  muscles 
at  the  base  of  the  head.  The  eighth  nerve,  the  auditory,  is  larger 
than  the  facial  and  arises  immediately  back  of  it. 

The  ninth  nerve,  the  glossopharyngeal,  which  arises  on  the  side 
of  the  medulla  close  to  the  auditory,  and  the  tenth  nerve,  the 
pneumogastric  or  vagus,  which  arises  close  to  the  glossopharyngeal, 
pass  out  of  the  skull  by  the  same  foramen.  Just  outside  of  the 
foramen  the  glossopharyngeal  merges  into  a  large  ganglion  from 
which  nerves  are  distributed  to  the  muscles  of  the  tongue  and 
the  base  of  the  skull.  The  pneumogastric  nerve  passes  straight 
back  along  the  side  of  the  neck  to  the  body  cavity,  where  it 
breaks  into  branches  which  supply  the  trachea,  lungs,  heart, 
stomach,  and  gizzard. 

The  eleventh  nerve,  the  spinal  accessory,  is  closely  joined  with 
the  vagus.  It  arises  on  the  side  of  the  spinal  cord  by  a  number 
of  roots,  enters  the  cranial  cavity  through  the  foramen  magnum, 
and  passes  out  again,  together  with  the  vagus  and  glossophar- 
yngeal, to  the  muscles  of  the  neck.  The  twelfth  cranial  nerve, 
the  hypoglossal,  arises  near  the  medial  line  on  the  ventral  sur- 
face of  the  medulla;  it  leaves  the  skull  by  a  foramen  at  its 
base  and  is  distributed  to  the  muscles  of  the  neck. 

Exercise  30.  Draw  a  view  of  the  lateral  aspect  of  the  brain  and 
the  cranial  nerves,  so  far  as  they  have  been  observed. 

Study  the  ventral  surface  of  the  brain.  Remove  the  brain 
from  the  head.  Just  behind  the  optic  chiasma  is  a  median  pro- 
jection of  the  thalamencephalon,  the  infundibulum ;  at  its  ventral 
end  is  the  pituitary  body,  or  hypophysis,  which  is  usually  torn  off 
when  the  brain  is  removed.  Back  of  the  infundibulum  are  the 
two  oculomotor  nerves ;  they  spring  from  the  midbrain  near 
the  median  line.  The  medulla  oblongata  extends  from  the  mid- 
brain  to  the  spinal  cord;  near  the  median  line  at  the  anterior 
end  of  the  medulla  will  be  seen  the  abducens  nerves. 

Exercise  31.  Draw  a  view  of  the  ventral  aspect  of  the  brain. 


THE  PIGEON  197 

Study  the  cavities  of  the  brain.  The  brain  is  a  hollow  struc- 
ture and  contains  a  series  of  cavities  which  are  a  continuation 
of  the  central  canal  of  the  spinal  cord.  The  cavities  of  the  two 
hemispheres  are  called  the  lateral  ventricles,  or  the  first  and  second 
ventricles.  Press  the  hemispheres  slightly  apart  and  cut  through 
the  thin  inner  and  postero-medial  wall  of  one  of  them  into  the 
ventricle.  Remove  a  portion  of  the  wall  and  observe  the  cavity. 
Note  the  large  white  mass  on  its  ventral  surface,  which  almost 
fills  it;  this  is  the  corpus  striatum.  In  the  medial  side  of  the 
posterior  wall  is  the  foramen  of  Monro,  by  which  the  lateral  ven- 
tricles communicate  with  each  other  and  with  the  third  ventricle, 
which  is  in  the  thalamencephalon. 

Remove  the  cerebellum  by  carefully  cutting  the  right  and  left 
peduncles,  which  join  it  with  the  medulla  on  each  side.  Connect- 
ing the  two  optic  lobes  will  be  seen  a  bridge  of  white  fibers 
called  the  optic  commissure;  in  front  of  this  is  the  roof  of  the 
third  ventricle  ;  behind  it  is  the  roof  of  the  fourth  ventricle. 
Remove  the  former  and  note  the  narrow  space,  the  third  ven- 
tricle, beneath,  the  thickened  lateral  walls  of  which  are  the  optic 
thalami.  Probe  the  ventricle  and  note  its  depth.  Cut  an  open- 
ing in  one  of  the  optic  lobes  and  note  its  ventricle.  Connecting 
the  third  and  the  fourth  ventricles  is  a  median  canal  called  the 
aqueductus  Sylvii ;  the  ventricle  of  the  optic  lobe  joins  it  on  each 
side.  The  fourth  ventricle  is  broad  and  shallow. 

Exercise  32.  Draw  a  diagram  showing  the  shape  and  position  of 
the  ventricles. 

The  muscular  system.  Kill  a  fresh  animal.  Make  a  midven- 
tral  slit  through  the  skin  from  the  mouth  to  the  anus,  and  skin 
the  ventral  surface  of  the  body,  including  the  wings  and  the 
legs.  In  order  to  avoid  cutting  the  muscles  and  other  organs 
beneath  the  skin,  make  this  incision  with  scissors,  lifting  up  the 
skin  with  forceps  and  then  cutting  it.  Take  special  care  not  to 
cut  the  large  thin-walled  crop  which  lies  in  contact  with  the 
skin  at  the  base  of  the  neck,  or  the  large  blood  vessels  and  nerves 
in  the  neck  and  the  wings.  Note  the  thinness  and  delicacy  of 
the  skin. 


198  VERTEBRATE  ZOOLOGY 

The  great  pectoral  muscles,  which  depress  the  wings  during 
flight,  form  a  large  part  of  the  breast.  They  lie  along  the 
entire  length  of  the  keel  of  the  breastbone  and  constitute  the 
lateral  and  anterior  surfaces  of  the  trunk.  A  prominent  tendon 
will  be  seen  running  through  the  midst  of  the  muscle  to  the 
shoulder  on  each  side ;  it  passes  over  the  shoulder  and  finds  its 
insertion  on  the  upper  and  outer  surface  of  the  humerus,  —  as 
will  be  seen  when  the  muscle  is  dissected. 

Posterior  to  the  pectoral  muscles  are  the  abdominal  muscles, 
which  form  the  ventral  and  lateral  body  walls  of  the  abdomen. 
In  the  midventral  line,  where  the  membranous  tendons  of  the 
abdominal  muscles  of  the  right  and  left  sides  meet,  is  a  prominent 
white  line,  the  linea  alba. 

Make  a  transverse  incision  in  the  middle  of  the  great  pectoral, 
dividing  it  into  an  anterior  and  a  posterior  half.  Be  careful  not 
to  cut  too  deeply,  as  the  lesser  pectoral  would  be  injured. 

Note  the  large  blood  vessels  in  the  muscle.  Beneath  the 
great  pectoral  lies  the  lesser  pectoral  muscle,  which  fills  the  angle 
between  the  keel  and  the  body  of  the  breastbone.  Remove  now 
that  portion  of  the  great  pectoral  back  of  this  incision  from  the 
body,  being  careful  not  to  cut  the  lesser  pectoral,  and  note  its 
attachment  to  the  ventral  portion  of  the  keel  and  the  lateral 
portions  of  the  body  of  the  breastbone.  Dissect  the  anterior 
half  of  the  great  pectoral,  from  the  incision  forward,  separating 
it  from  the  lesser  pectoral,  the  breastbone,  and  the  clavicle  (the 
wishbone),  until  the  large  tendon  at  its  forward  end  is  reached. 
Be  careful  in  doing  this  not  to  cut  or  injure  any  of  the  bones. 
Follow  the  tendon  to  its  insertion  in  the  dorsal  side  of  the 
humerus.  A  broad  shoulder  muscle,  the  anterior  head  of  the 
biceps,  covers  this  tendon. 

Note  the  tendon  which  runs  through  the  middle  of  the  lesser 
pectoral  muscle  to  the  shoulder.  Free  the  muscle  from  its 
attachment  to  the  breastbone  and  the  coracoid,  which  is  the 
large  bone  joining  the  breastbone  with  the  shoulder  blade,  and 
follow  the  tendon  to  its  insertion  in  the  dorsal  side  of  the 
humerus.  Be  careful  not  to  injure  any  of  these  bones  while 
dissecting  the  muscles. 


THE  PIGEON  199 

Test  the  action  of  both  pectoral  muscles ;  the  great  pectoral 
will  be  seen  to  depress  the  wing,  and  the  lesser  pectoral,  to 
raise  it. 

The  abdominal  muscles  are  of  much  smaller  extent  in  birds 
than  in  mammals,  on  account  of  the  large  size  of  the  breast 
muscles.  They  consist  of  the  right  and  left  external  obliques, 
which  form  the  outer  surface  of  the  abdomen  and  whose  fibers 
run  diagonally ;  the  internal  obliques,  which  lie  beneath  the  exter- 
nal obliques  and  whose  fibers  run  at  right  angles  to  their  fibers ; 
the  transverse  muscles,  which  are  the  innermost  and  whose  fibers 
run  transversely ;  and  the  rectus  abdominis  muscles,  which  occupy 
the  median  area.  All  of  these  muscles  are  more  or  less  rudi- 
mentary and  tendinous,  their  fibers  having  disappeared  and  the 
membranous  fascisB  and  tendons  alone  being  present  in  portions 
of  them.  The  rectus  abdominis  has  entirely  lost  the  metamer- 
ism which  characterizes  it  in  amphibians  and  mammals.  These 
muscles  will  not  be  dissected.  Observe  as  many  of  these  fea- 
tures as  possible. 

On  the  ventral  side  of  the  head  note  the  submandibular  muscle, 
the  fibers  of  which  run  transversely  across  the  throat ;  its  median 
portion  is  tendinous. 

In  the  proximal  division  of  the  wing  (the  upper  arm)  are  the 
large  biceps  muscle  on  the  anterior  side  and  the  large  triceps  on  the 
posterior  side ;  these  muscles  act  as  the  chief  flexor  and  extensor 
respectively  of  the  forearm. 

In  the  middle  division  (the  forearm)  the  following  muscles 
appear  on  the  ventral  surface,  beginning  with  the  anterior 
border :  the  extensor  radialis,  the  pronator  brevis,  the  pronator  longus, 
the  distal  end  only  of  which  appears,  the  short  cubitocarpalis 
profundus,  the  long  extensor  carpi  ulnaris,  and  the  large  flexor  carpi 
ulnaris  which  forms  the  posterior  border.  Determine,  by  follow- 
ing the  tendons,  which  of  these  muscles  extend  and  which  flex 
the  hand. 

In  the  ventral  surface  of  the  proximal  division  of  the  leg  (the 
thigh),  beginning  at  the  anterior  border,  are  the  large  sartorius 
muscle  which  forms  this  border,  the  much  smaller  ilio-tibialis, 
a  variable  portion  of  the  distal  end  of  the  femoro-tibialis,  the 


200  VERTEBKATE  ZOOLOGY 

very  broad  pubo-ischio-femoralis  which  forms  the  middle  portion 
of  the  thigh,  the  semimembranosus,  and  the  semitendinosus  which 
forms  the  posterior  border  of  the  thigh. 

On  the  ventral  surface  of  the  middle  division  of  the  leg  (the 
shank)  are  the  tibialis  muscle,  which  forms  its  anterior  portion, 
and  the  gastrocnemius,  which  forms  its  posterior  portion. 

Determine  so  far  as  possible  which  of  these  leg  muscles  are 
extensors  and  which  are  flexors. 

Exercise  33.  Draw  an  outline  of  the  ventral  aspect  of  the  animal 
and  place  in  it  those  muscles  which  have  been  observed. 

The  skeletal  system.  This  is  made  up  of  the  exoskeleton  and 
the  endoskeleton.  The  exoskeleton  is  composed  of  certain  special 
integumentary  structures,  —  the  feathers,  the  horny  covering  of 
the  bill,  and  the  scales  and  claws  of  the  feet ;  the  endoskeleton 
is  the  bony  and  cartilaginous  framework  of  the  body. 

The  exoskeleton.  Three  kinds  of  feathers  are  present,  —  the 
contour  feathers,  the  down  feathers,  and  the  filoplumes  or  pin- 
feathers, —  which  have  been  described  on  page  166.  Study  the 
structure  of  a  contour  feather.  It  is  made  up  of  two  portions,  — 
the  quill,  the  proximal,  cylindrical  portion  which  projects  from 
the  skin;  and  the  vane,  the  distal  flattened  portion.  The  quill 
is  hollow  and  has  two  openings,  —  one  at  the  proximal  end,  the 
inferior  umbilicus;  and  one  at  the  base  of  the  vane,  the  superior 
umbilicus. 

The  vane  is  composed  of  a  central  axis,  the  shaft,  —  the  con- 
tinuation of  the  quill,  —  which  is  solid  and  is  square  in  cross 
section ;  the  barbs,  lateral  outgrowths  of  the  shaft ;  and  the 
barbules,  minute  projections  of  the  barbs.  The  barbules  are 
usually  provided  with  hooklike  outgrowths  which  enable  the 
overlapping  barbules  of  contiguous  barbs  to  take  firm  hold  of 
one  another  and  so  convert  the  vane  into  an  unbroken  surface. 
At  the  base  of  the  vane  these  hooks  are  absent. 

Exercise  34.  Draw  a  sketch  of  a  contour  feather  showing  the 
quill,  vane,  shaft,  and  barbs.  Draw  also  one  or  two  barbs, 
with  their  barbules  and  hooks,  as  seen  under  a  microscope. 


THE  PIGEON  201 

In  down  feathers  there  is  either  no  shaft,  —  the  barbs  arising 
from  the  distal  end  of  the  quill,  — or  the  shaft  is  very  rudimen- 
tary ;  no  hooks  are  present.  In  the  filoplumes  the  barbs  are  either 
absent  or  are  present  in  a  rudimentary  condition. 

Exercise  35.  Draw   a  down   feather   much   enlarged.    Draw  a 
nloplume. 

The  endoskeleton  is  the  inner  framework  of  the  body  and  is 
made  up  of  bone  and  cartilage.  It  may  be  divided  into  (1)  the 
axial  skeleton,  which  includes  the  skull  and  the  vertebral  column, 
with  the  ribs  and  the  sternum,  and  (2)  the  appendicular  skeleton, 
which  forms  the  framework  of  the  extremities. 

To  prepare  the  internal  skeleton  for  study,  open  the  abdomi- 
nal cavity,  without  injuring  any  of  the  bones,  and  remove 
all  the  viscera.  The  body  should  then  be  boiled  a  short  time 
until  the  skin  and  muscles  can  be  easily  removed.  Do  not  boil 
it  so  long  that  the  skeleton  falls  apart.  If  the  neck  vertebrae 
show  a  tendency  to  become  separated  from  one  another,  they 
had  better  be  strung  on  a  string.  The  head  should  be  taken 
from  the  neck,  and  care  taken  not  to  lose  the  lower  jaw  or 
the  hyoid  apparatus  which  lies  in  the  floor  of  the  mouth  and 
supports  the  tongue.  Care  must  be  taken  also  that  the  bones 
of  the  legs  and  wings,  and  of  the  uropygium,  do  not  become 
separated. 

Observe  the  general  character  of  the  skeleton.  It  is  distin- 
guished by  great  lightness,  almost  all  the  bones  being  hollow 
or  spongy,  instead  of  compact  or  filled  with  marrow.  It  is  also 
distinguished  by  great  rigidity,  the  bones  having  a  decided 
tendency  to  ankylose. 

The  appendicular  skeleton;  the  anterior  extremities.  These 
consist  of  the  pectoral  girdle  and  the  wings.  The  pectoral  or 
shoulder  girdle  is  a  strong  structure  which  forms  the  connec- 
tion between  the  skeleton  of  the  wings  and  the  trunk ;  during 
flight  the  body  of  the  bird  is  supported  in  the  air  by  the  wings, 
and  it  is  important  that  this  connection  be  a  strong  and  yet 
an  elastic  one.  The  girdle  is  composed  of  a  right  and  a  left 
half,  which  are  joined  ventrally  by  the  sternum  or  breastbone. 


202  VERTEBRATE  ZOOLOGY 

Each  half  consists  of  three  bones,  —  the  scapula,  the  clavicle,  and 
the  coracoid.  Of  these  bones  the  first  named  is  dorsal  in  posi- 
tion ;  the  other  two  are  ventral,  —  the  clavicle  being  anterior  to 
the  coracoid.  The  glenoid  cavity,  in  which  the  humerus  articu- 
lates, is  situated  at  the  meeting  point  of  the  scapula  and  the 
coracoid. 

The  scapulae  are  a  pair  of  elongated,  flattened  bones  which 
lie  along  the  spinal  column,  attached  to  it  and  to  the  ribs  by 
means  of  muscles.  The  coracoids  are  a  pair  of  thick  bones  which 
lie  at  right  angles  to  the  scapulae  and  extend  between  them 
and  the  anterior  end  of  the  breastbone ;  they  are  firmly  joined 
with  both  the  scapulae  and  the  breastbone.  This  connection 
is  a  very  important  one,  inasmuch  as  the  greater  part  of  the 
viscera  lie  in  the  concave  dorsal  surface  of  the  breastbone. 
Note  above  the  glenoid  cavity  the  foramen  triosseum,  an  opening 
formed  by  the  meeting  of  a  process  from  the  scapula  and  one 
from  the  coracoid.  The  tendon  of  the  lesser  pectoral  muscle 
passes  through  it. 

The  clavicles  are  ankylosed  at  their  ventral  ends  and  form 
the  wishbone.  Their  dorsal  ends  articulate  with  the  coracoids ; 
their  ankylosed  ventral  ends  are  joined  by  a  ligament  with  the 

keel  of  the  breastbone. 

• 

Exercise  36.  Draw  the  pectoral  girdle,  with  the  anterior  end  of 
the  breastbone. 

The  skeleton  of  the  wing  is  made  up  of  three  divisions,  —  a 
proximal,  a  middle,  and  a  distal  division.  The  proximal  divi- 
sion is  composed  of  a  single  bone,  —  the  humerus.  The  head  of 
this  bone  is  made  up  of  the  rounded  articular  surface,  which 
fits  into  the  glenoid  cavity,  and  of  a  small  anterior  and  a  large 
posterior  tuberosity.  The  anterior  tuberosity  is  continuous  with 
the  prominent  deltoid  ridge  in  which  is  inserted  the  great  pectoral 
muscle.  In  the  great  tuberosity  is  the  pneumatic  foramen,  an 
opening  into  the  hollow  center  of  the  bone.  The  distal  end  of 
the  bone  has  two  articular  surfaces,  an  anterior  one  for  the 
radius  and  a  transverse,  posterior  one  for  the  ulna. 


THE  PIGEON  203 

The  middle  division  is  formed  by  the  radius  and  ulna,  of  which 
the  latter  is  somewhat  longer  and  thicker  than  the  former.  At 
the  proximal  end  of  the  ulna  is  the  short  olecranon  process,  which 
forms  the  elbow.  Along  the  posterior  border  of  the  ulna  is  a 
row  of  small  elevations  which  mark  the  position  of  the  base  of 
the  secondary  wing  quills. 

The  distal  division  is  made  up  of  the  wrist  and  the  hand. 
The  carpal  or  wrist  bones  are  much  modified,  but  two  free  bones 
being  present,  the  radial  and  the  ulnar,  which  are  at  the  distal 
ends  of  the  radius  and  ulna  respectively. 

•  The  bones  of  the  hand  fall  into  two  groups,  the  proximal 
carpo-metacarpus  and  the  distal  digits.  The  carpo-metacarpus  is  a 
large  arched  bone  which  is  formed  by  the  fusion  of  the  distal 
carpal  bones  with  the  first,  second,  and  third  metacarpals.  The 
digits  are  also  three  in  number.  The  first,  or  thumb,  is  short  and 
possesses  free  movement ;  it  is  situated  at  the  base  of  the  carpo- 
metacarpus  and  consists  of  two  phalanges,  the  distal  phalanx 
being  very  small.  The  second  digit  is  the  longest  and  has  three 
phalanges ;  the  third  has  a  single  phalanx. 

Exercise  37.  Draw  the  bones  of  the  wing. 

The  posterior  extremities.  These  consist  of  the  pelvic  girdle 
and  the  legs.  The  pelvic  girdle  is  very  large  and  is  firmly 
ankylosed  with  fourteen  or  fifteen  vertebrae,  forming  a  solid 
support  for  the  legs.  The  pelvic  girdle  is  composed  of  a  right 
and  a  left  innominate  bone,  each  of  which  has  been  formed  by  the 
fusion  of  three  bones,  —  the  ilium,  ischium,  and  pubis.  At  the 
meeting  point  of  these  bones  is  the  acetabulum,  the  depression  in 
which  the  head  of  the  femur  articulates. 

The  ilium  is  the  largest  of  the  pelvic  bones.  It  is  a  large, 
flat  bone,  dorsal  in  position,  and  is  fused  along  its  entire  length 
with  the  vertebral  column ;  it  is  divided  into  two  parts,  an 
anterior  and  a  posterior,  the  former  of  which  is  concave  and 
the  latter  convex  dorsally. 

The  ischium  and  the  pubis  are  both  ventral  to  the  acetabulum, 
the  latter  being  anterior  and  ventral  to  the  former.  The  ischium 
is  larger  than  the  pubis  and  is  separated  from  the  ilium  at  its 


204  VERTEBRATE  ZOOLOGY 

forward  end  by  a  large  opening,  the  iliosciatic  foramen.  The  pubis 
is  long  and  slender  and  is  separated  from  the  ischium  by  the 
long  and  narrow  obturator  foramen. 

Exercise  38.  Draw  the  dorsal  and  lateral  aspect  of  the  innomi- 
nate bone. 

The  skeleton  of  the  leg  is  made  up  of  three  divisions, — a 
proximal,  a  middle,  and  a  distal  division.  The  proximal  division 
is  composed  of  a  single  bone,  the  femur,  which  articulates  in 
the  acetabulum.  On  the  outer  side  of  the  head  of  the  bone  is 
a  ridge,  the  great  trochanter.  The  patella  —  a  small  bone  which  is 
present  in  the  tendons  passing  over  the  knee  —  lies  in  front 
of  the  distal  or  lower  end  of  the  femur ;  it  is  usually  lost  when 
the  leg  is  cleaned. 

The  middle  division  is  composed  of  two  bones,  the  tibio-tarsus 
and  the  fibula ;  the  first  is  a  large  bone  which  has  been  formed  by 
the  fusion  of  the  tibia  with  the  proximal  tarsal  or  ankle  bones  ;  the 
second  is  a  slender  bone  which  is  often  fused  with  the  first. 

The  distal  division  is  composed  of  the  bones  of  the  foot.  They 
fall  into  two  groups,  —  a  vertical  shaft,  the  tarso-metatarsus,  and 
the  toes  or  digits.  The  tarso-metatarsus  is  formed  by  the  fusion 
of  the  distal  tarsal  or  ankle  bones  with  the  second,  third,  and 
fourth  metatarsal  bones.  The  boundaries  of  the  three  metatar- 
sals  are  easily  distinguished.  No  free  tarsal  bones  are  present,  — 
the  proximal  row  being  fused  with  the  tibia,  as  just  stated,  to 
form  the  tibio-tarsus ;  the  distal  row,  with  the  metatarsals  to 
form  the  tarso-metatarsus. 

Four  digits  are  present.  The  first  digit,  which  corresponds  to 
the  big  toe,  projects  backward  and  is  raised  above  the  ground. 
It  is  composed  of  the  first  metatarsal  bone,  which  is  very  small, 
and  two  phalanges.  The  second  digit  is  the  innermost  of  the 
three  projecting  forward;  it  has  three  phalanges.  The  third 
digit  has  four  phalanges  and  the  fourth  digit  has  five. 

Exercise  39.  Draw  an  outline  of  the  bones  of  the  leg  and  foot. 

The  axial  skeleton.  This  is  composed  of  the  skull  and  the 
vertebral  column,  with  the  ribs  and  the  sternum.  The  vertebral 


THE  PIGEON  205 

column  consists  of  a  succession  of  vertebrae  which  may  be  divided 
into  the  following  regions :  the  cervical,  thoracic,  lumbar,  sacral, 
and  caudal.  The  boundaries  separating  these  regions  in  birds 
are  not  definite  but  are  more  or  less  arbitrary.  The  vertebrae  of 
all  except  the  cervical  region  show  a  marked  tendency  to  fuse 
together ;  the  cervical  region,  on  the  other  hand,  is  characterized 
by  great  flexibility. 

Each  vertebra  is  composed  essentially  of  the  following  parts : 
the  centrum,  which  forms  its  body ;  the  neural  arch,  which  rises 
from  the  dorsal  surface  of  the  centrum  and  is  composed  of 
the  two  neural  processes  and  the  neural  spine ;  the  paired  transverse 
processes,  which  project  laterally  or  ventrolaterally  from  its  sides. 

The  cervical  vertebrae  are  fourteen  in  number.  Study  these 
and  note  carefully  their  variations  of  structure.  The  centrum 
is  elongated.  Its  ends  are  saddle-shaped,  the  anterior  end  being 
convex  dorsoventrally  and  concave  laterally,  while  the  posterior 
end  is  concave  dorsoventrally  and  convex  laterally.  The  trans- 
verse process  projects  back  from  the  anterior  portion  of  the 
centrum  on  each  side,  and  is  prolonged  into  a  short  spine. 
At  the  base  of  the  process  is  a  prominent  foramen,  and  the 
series  of  these  foramina  in  the  successive  cervical  vertebrae  form 
the  vertebrarterial  canal,  in  which  the  vertebral  artery  and  vein 
and  the  sympathetic  nerve  lie.  The  transverse  process  and  its 
spine  are  not  strictly  homologous  to  the  transverse  processes  of 
the  other  vertebras,  but  are  equivalent  to  a  rib  plus  the  process. 
The  foramen  lies  between  the  head  of  the  rib  and  the  process. 
Besides  these  rudimentary  cervical  ribs  two  pairs  of  free  ribs 
are  present  on  the  last  two  cervical  vertebrae ;  they  do  not  reach 
the  sternum. 

Projecting  from  both  the  anterior  and  the  posterior  end  of  the 
neural  arches  are  two  small  processes  by  which  the  successive 
vertebrae  articulate  with  one  another.  These  are  called  the 
prezygapophyses  and  postzygapophyses,  the  former  projecting  from 
the  anterior  end  of  the  vertebra  and  articulating  with  the  latter 
on  the  vertebra  in  front  of  it. 

The  first  two  cervical  vertebrae  are  called  the  atlas  and  the 
axis;  they  support  the  skull  and  differ  in  structure  from  the 


206  VEKTEBBATE   ZOOLOGY 

others.  The  atlas  is  a  ring-shaped  bone  in  which  the  centrum 
and  the  neural  spine  are  absent,  and  the  transverse  processes 
are  broad,  winglike  projections.  On  its  anterior  face  is  a  median 
groove ;  into  this  fits  the  condyle  by  which  the  skull  articulates 
with  the  spinal  column.  On  its  posterior  face  is  also  a  median 
groove  in  which  lies  the  odontoid  process  of  the  axis.  These 
grooves  are  bounded  dorsally  by  a  transverse  ligament  which 
separates  them  from  the  neural  canal. 

The  axis  is  an  elongated  vertebra,  projecting  from  the  anterior 
end  of  which  is  the  cylindrical  odontoid  process;  this  process  is 
equivalent  to  the  centrum  of  the  atlas. 

Exercise  40.  Draw  the  lateral  aspect  of  the  sixth  cervical  ver- 
tebra on  a  scale  of  2 ;  draw  the  anterior  aspect. 

Exercise  41.  Draw  the  anterior  aspect  of  the  atlas  on  a  scale  of  2. 

Exercise  42.  Draw  the  lateral  aspect  of  the  atlas  and  axis  on  a 
scale  of  2. 

The  thoracic  vertebrae  are  five  in  number,  being  those  which  are 
joined  with  the  sternum  by  ribs.  They  are  all  fused  together, 
and  with  the  lumbar  vertebrae.  The  posterior  thoracic  vertebra 
is  also  fused  with  the  pelvis. 

The  three  lumbar  vertebrae,  the  four  sacral  vertebrae,  and  the  ante- 
rior six  caudal  vertebrae  are  all  fused  with  one  another  and  with 
the  pelvis.  These  vertebrae,  together  with  the  fifth  thoracic 
vertebra,  form  what  is  called  the  synsacrum. 

Note  carefully  the  character  of  these  fused  vertebrae,  espe- 
cially of  their  transverse  processes.  Note  the  intervertebral 
foramina  through  which  the  spinal  nerves  pass. 

The  free  caudal  vertebrae  are  six  in  number.  The  spinal  column 
ends  posteriorly  with  the  pygostyle,  an  irregular  bone  formed  by 
the  fusion  of  several  vertebras. 

The  ribs.  The  first  two  ribs  articulate  with  the  last  two  cer- 
vical vertebrae  and  do  not  reach  the  sternum.  Each  has  two 
articular  surfaces,  —  the  head  or  capitulum,  which  articulates  with 
the  centrum;  and  the  tuberculum,  which  articulates  with  the 
transverse  process.  The  posterior  five  ribs  articulate  with  the 


THE  PIGEON  207 

thoracic  vertebrae  and  also  with  the  sternum.  Each  thoracic  rib 
has  two  portions,  —  a  dorsal  vertebral  portion  and  a  ventral 
sternal  portion,  which  articulate  with  each  other.  Projecting 
backward  from  the  vertebral  portions  of  all  the  ribs  except  the 
first  and  the  last  is  the  prominent  uncinate  process. 

The  sternum,  or  breastbone,  is  a  large  flat  bone  which  extends  far 
back  of  the  ribs  and  covers  the  ventral  side  of  the  breast  and  a 
large  part  of  the  abdomen.  On  its  ventral  surface  is  the  keel, 
which  projects  ventrally  in  the  median  plane.  Inasmuch  as  the 
principal  muscles  of  flight  have  their  origin  in  the  sternum,  the 
size  of  these  muscles  and  consequently  the  powers  of  flight  are 
directly  correlated  with  the  size  of  the  sternum.  Birds  which 
do  not  fly,  as  the  ostrich,  have  a  very  small  sternum,  on  which 
there  is  often  no  keel.  Projecting  from  the  lateral  edge  of  the 
sternum  on  each  side  near  its  middle  is  the  prominent  middle 
xiphoid  process.  Behind  this  is  a  deep  notch,  and  behind  that,  the 
small  external  xiphoid  process  which  fuses  posteriorly  with  the  body 
of  the  sternum,  inclosing  a  small  opening.  In  front  of  the 
middle  xiphoid  processes  are  the  articular  surfaces  of  the  ribs,  and 
at  the  anterior  end  of  the  sternum  those  of  the  coracoid  bones. 

Exercise  43.  Draw  a  lateral  view  of  the  thorax,  showing  the 
thoracic  vertebrae,  the  ribs,  and  the  sternum. 

Exercise  44.  Draw  a  ventral  view  of  the  sternum. 

The  skull.  The  skull  is  made  up  of  two  portions,  — the  cranium 
and  the  viscerai  skeleton.  The  former  protects  the  brain  and  the 
organs  of  special  sense ;  the  latter  forms  the  framework  of  the 
face,  the  beak,  and  the  tongue. 

The  cranium  —  which  forms  the  entire  top  and  back  part  of 
the  skull  —  is  characterized  by  the  great  lightness  of  the  bones 
composing  it  and  their  tendency  to  become  ankylosed.  They  are 
not  compact  but  are  spongy ;  the  air  cells  in  them  can  be  seen 
through  the  outer  wall  by  holding  the  cranium  up  to  the  light. 
In  an  old  bird  ankylosis  has  gone  on  so  far  that  the  sutures 
marking  the  boundaries  of  the  bones  have  largely  disappeared ; 
in  a  young  bird,  however,  they  are  still  present. 


208  VEKTEBKATE  ZOOLOGY 

The  visceral  skeleton,  which  forms  the  ventral  part  of  the 
skull,  is  also  characterized  by  the  lightness  and  delicacy  of  its 
bones  and  the  absence  of  teeth.  It  is  much  less  firmly  joined 
with  the  cranium  than  in  mammals.  Care  must  be  taken  to 
preserve  the  lower  jaw  and  the  hyoid  apparatus. 

Study  the  posterior  surface  of  the  skull.  The  large  circular 
foramen  magnum  is  seen  here,  through  which  the  spinal  cord  joins 
the  brain.  Beneath  it  is  the  occipital  condyle,  by  which  the  skull 
articulates  with  the  atlas ;  note  carefully  its  shape.  The  hinder 
end  of  the  skull  is  formed  by  four  bones  in  the  young  bird, — the 
basioccipital  —  beneath  and  in  front  of  the  foramen  magnum,  the 
paired  exoccipitals  at  the  sides,  and  the  supraoccipital  dorsal  to  it. 

A  more  or  less  prominent  semicircular  ridge,  called  the  lamb- 
doidal  crest,  in  which  certain  muscles  of  the  neck  are  inserted, 
runs  across  the  hinder  end  of  the  skull,  separating  the  occip- 
ital from  the  parietal  region;  at  each  end  of  this  crest  is  the 
tympanic  cavity. 

Study  the  dorsal  surface  of  the  skull.  Its  roof  is  formed  by 
three  pairs  of  large  membrane  bones,  the  parietals,  frontals,  and 
nasals.  The  parietals  are  the  hindermost,  —  the  suture  between 
them  and  the  frontals  being  in  the  young  bird  at  the  hinder 
border  of  the  orbit.  The  frontals  form  the  portion  of  the  roof 
between  the  orbits,  —  the  suture  between  them  and  the  nasals 
being  at  the  forward  border  of  the  orbits.  The  nasals  extend 
forward  from  the  anterior  end  of  the  frontals  and  form  the  base 
of  the  beak ;  each  one  of  them  sends  a  long  process  along  each 
side  of  one  of  the  nostrils. 

In  front  of  the  nasals  are  the  premaxillae,  which  form  the  ante- 
rior portion  of  the  beak  and  belong  to  the  visceral  skeleton. 
Each  premaxilla  is  composed  of  three  parts,  which  meet  in  the 
tip  of  the  beak,  —  the  nasal  process  and  maxillary  process,  which  lie 
on  the  inner  and  outer  side  of  the  nasal  opening  respectively, 
and  the  small  palatine  process,  which  forms  the  anterior  part  of 
the  roof  of  the  mouth. 

Exercise  45.  Draw  the  posterior  aspect  of  the  skull  on  a  scale  of  2. 
Exercise  46.  Draw  the  dorsal  aspect  of  the  skull. 


THE  PIGEON  209 

Study  the  lateral  surface  of  the  skull.  Note  the  very  large 
orbit.  In  the  hinder  part  of  the  skull  will  be  seen  the  lambdoidal 
ridge  and  the  tympanic  cavity.  Between  this  cavity  and  the  parie- 
tal on  each  side  is  the  large  squamosal  bone,  which  forms  the 
posterior  border  of  the  orbit. 

The  tympanic  cavity  is  a  circular  depression,  within  the  margin 
of  which  is  the  tympanic  membrane  or  eardrum.  On  the  inner 
wall  of  the  cavity  are  two  foramina,  the  fenestra  ovalis  and  the 
fenestra  rotunda,  the  former  of  which  is  dorsal  to  the  latter  and 
is  closed  by  the  stapes,  the  innermost  of  the  two  ear  ossicles. 
The  stapes  articulates  with  the  columella,  —  the  outermost  and 
larger  of  these  ossicles,  —  which  is  a  rod  of  bone  and  cartilage 
extending  to  the  inner  surface  of  the  tympanic  membrane.  At 
the  anterior  end  of  the  tympanic  cavity  is  the  opening  of  the 
Eustachian  tube,  which  places  the  cavity  in  communication  with 
the  pharynx.  Probe  it  with  a  bristle. 

Projecting  forward  from  the  anterior  border  of  the  squamosal 
are  two  short  processes,  the  more  dorsal  being  the  zygomatic 
process ;  the  more  ventral  articulates  with  a  thick,  irregular  bone, 
the  quadrate.  This  bone  is  the  suspensorium  of  the  jaws  on  each 
side,  i.e.,  it  connects  them  with  the  cranium ;  both  upper  and 
lower  jaws  articulate  with  the  ventral  and  anterior  surfaces  of 
it,  as  will  be  seen  later.  The  quadrates  are  not  tightly  joined 
with  the  remainder  of  the  skull,  but  articulate  freely  with  it. 
The  jaws  are  thus  joined  with  the  cranium  by  a  double  articu- 
lation on  each  side. 

In  front  of  and  above  the  tympanic  cavity  and  medial  to  the 
quadrate  bone  is  the  trigeminal  foramen,  through  which  the  tri- 
geminal  nerve  passes. 

The  orbit  is  a  very  large  cavity  which  is  bounded  behind  by 
the  squamosal  and  the  alisphenoid,  the  latter  bone  being  in  front 
of  the  former;  above,  it  is  bounded  by  the  large  frontal  bone, 
—  which  forms  the  whole  roof  of  the  skull  between  the  orbits, — 
and  in  front  by  the  frontal  and  the  lachrymal,  the  latter  bone 
forming  its  anterior  border.  The  inner  wall  of  the  two  orbits, 
the  interorbital  septum,  is  formed  by  the  fusion  of  the  presphenoid 
and  orbitosphenoid  posteriorly,  the  elongated  rostrum  ventrally, 


210  VEETEBEATE  ZOOLOGY 

and  the  mesethmoid  anteriorly.  The  ventral  wall  of  the  orbit  is 
almost  entirely  lacking. 

In  the  hinder  part  of  the  orbit  is  the  large  optic  foramen 
through  which  the  optic  nerve  enters  it ;  just  back  of  this  are 
the  foramina  of  the  oculomotor  and  the  trochlear  nerves. 

Anterior  to  the  frontals  are  the  nasal  and  premaxillary  bones, 
which  have  been  already  described. 

Extending  back  on  each  side  from  the  premaxilla  to  the  quad- 
rate is  a  slender  bar  which  is  composed  of  three  bones  fused 
together,  the  hinder  part  being  the  quadratojugal,  the  middle  part 
the  jugal,  and  the  small  forward  end  the  maxillary.  Medial  to  this 
bar  the  quadrate  is  joined  with  the  premaxilla  by  a  second  row 
of  bones  consisting  of  the  pterygoid  and  the  palatine,  the  former 
articulating  with  the  quadrate,  the  latter  with  the  premaxilla. 

The  lower  jaw,  or  mandible,  is  a  bony  arch  which  is  composed 
of  five  pairs  of  bones  fused  together.  The  hinder  end  on  each 
side  is  formed  by  the  articular  bone,  which  articulates  with  the 
quadrate.  The  articular  is  an  ossification  of  the  proximal  end 
of  Meckel's  cartilage,  which  in  the  embryo  forms  the  whole  of 
the  lower  jaw.  This  cartilage  persists  in  the  adult  but  is  cov- 
ered with  membrane  bones.  These  are  the  dentary,  the  largest 
of  the  bones  of  the  mandible,  which  forms  the  anterior  half  of 
each  side;  the  supra-angular,  which  forms  the  dorsal  portion  of 
the  posterior  half ;  and  the  angular,  which  is  a  small  bone  on  the 
inner  side  of  the  posterior  portion. 

Exercise  47.  Draw  the  lateral  aspect  of  the  skull  on  a  scale  of  2. 

Study  the  ventral  surface  of  the  skull  after  the  lower  jaw  has 
been  removed.  At  the  hinder  end  is  the  basioccipital  bearing 
the  condyle.  Covering  the  base  of  the  cranium  between  the 
tympanic  cavities  is  a  large  membrane  bone,  the  basitemporal, 
which  represents  the  posterior  portion  of  the  parasphenoid  of 
lower  vertebrates.  This  bone  entirely  covers  the  basisphenoid 
and,  in  old  birds,  is  fused  with  it.  In  front  of  it  is  an  elongated 
membrane  bone,  the  rostrum,  which  represents  the  anterior  por- 
tion of  the  parasphenoid.  It  covers  and  is  fused  with  the  pre- 
sphenoid,  mesethmoid,  and  the  orbitosphenoids. 


THE  PIGEON  211 

A  number  of  foramina  pierce  the  base  of  the  skull.  On  each 
side  of  the  occipital  condyle  is  the  foramen  of  the  hypoglossal 
nerve,  and  lateral  to  it  is  the  common  foramen  of  the  glosso- 
pharyngeal,  vagus,  and  spinal  accessory  nerves.  In  front  of 
these  is  the  foramen  of  the  facial  nerve. 

The  upper  jaw  will  be  seen  to  be  composed  of  two  paired 
rows  of  bones,  —  an  outer  and  an  inner  one,  —  which  meet,  on 
each  side,  at  the  quadrate  bone  posteriorly  and  at  the  premax- 
illa  anteriorly.  The  outer  row  is  composed  of  the  maxillae,  the 
jugals,  and  the  quadratojugals ;  the  inner  row,  of  the  ptery- 
goids  and  the  palatines.  The  pterygoid  is  a  short  bone  which 
articulates  with  the  inner  surface  of  the  quadrate  and  with 
the  rostrum.  The  palatine  is  a  long  bone  which  extends  for- 
ward from  the  pterygoid,  its  hinder  portion  being  broad,  its 
anterior  portion  slender.  Note  carefully  the  relation  of  all  these 
bones  to  one  another. 

Exercise  48.  Draw  the  ventral  aspect  on  a  scale  of  2,  and  care- 
fully label  all  these  characters. 

The  bones  of  the  cranium,  which  have  just  been  studied,  fall 
into  two  categories,  —  those  forming  the  cranium  proper  or  brain 
case,  and  those  forming  the  special  sense  capsules.  The  follow- 
ing bones  belong  to  the  cranium  proper  or  brain  case :  the  occip- 
itals,  the  sphenoids,  and  the  ethmoid,  which  are  cartilage  bones ; 
and  the  parietals,  f rentals,  basitemporal,  and  rostrum,  which  are 
membrane  bones.  The  special  sense  capsules  are  three  in  number. 
The  auditory  capsule  is  formed  by  three  cartilage  bones,  —  the 
prootic,  opisthotic,  and  epiotic,  —  all  of  which  in  the  adult  bird 
are  fused  with  other  bones.  The  prootic,  in  which  the  largest 
part  of  the  auditory  capsule  is  lodged,  is  fused  with  the  squa- 
mosal,  a  large  membrane  bone  which  forms  a  part  of  the  wall 
of  the  brain  case.  The  epiotic  fuses  with  the  supraoccipital,  and 
the  opisthotic  with  the  exoccipital.  The  optic  capsule  does  not 
ossify,  but  the  lachrymal  —  a  membrane  bone  —  develops  in  con- 
nection with  it  and  forms  a  part  of  the  anterior  wall  of  the 
orbit.  Besides  these,  a  row  of  small  membrane  bones  called 
the  sclerotic  plates  appear  in  the  sclera  around  the  cornea.  The 


212  VEKTEBKATE  ZOOLOGY 

nasal  capsule  is  formed  by  the  mesethmoid,  the  nasals,  and 
the  vomer. 

The  remaining  bones  of  the  skull,  which  form  the  upper  and 
lower  jaws,  the  suspensorium,  and  the  hyoid  apparatus,  belong 
to  the  visceral  skeleton. 

Study  the  hyoid  apparatus.  It  is  composed  of  a  jointed  median 
body,  and  two  pairs  of  slender  projections  called  the  horns  or 
cornua.  The  body  is  composed  of  three  pieces.  The  anterior 
piece  —  the  basihyal  —  is  the  largest  and  is  shaped  like  an  arrow- 
head. It  is  partly  cartilaginous  and  partly  bony,  and  from  its 
hinder  end  extends  a  pair  of  short  projections,  —  the  anterior 
cornua.  The  middle  piece  is  of  bone,  and  from  its  hinder  end 
extends  a  pair  of  long,  slender  projections,  —  the  posterior  cornua, 
—  which  are  composed  principally  of  bone  and  are  jointed. 
The  posterior  piece  is  composed  of  bone  and  cartilage. 

Exercise  49.  Draw  the  hyoid  apparatus. 


CHAPTER  V 
MAMMALS 
THE  CAT 

Two  or  three  specimens  will  be  needed  for  a  complete  dis- 
section of  the  cat,  —  one  for  the  muscles  and  skeleton,  and 
one  or  two  for  the  remaining  organs.  They  should  be  killed 
with  chloroform  or  ether,  as  needed,  and  preserved  in  cold 
storage  or  in  formalin.  If  the  weather  be  not  too  hot,  it  is  an 
excellent  plan  to  pin  the  skin  tightly  over  the  body  and  keep 
it  in  a  cool  place  when  it  is  not  being  dissected.  As  soon  as  it 
begins  to  smell  it  should  be  completely  skinned,  with  the  excep- 
tion of  the  feet  and  head,  and  preserved  in  a  solution  of  half  a 
per  cent  or  one  per  cent  formalin.  The  body  must  always  be  com- 
pletely covered  by  the  fluid,  and  the  latter  must  be  changed  as 
often  as  it  becomes  stale.  A  stronger  solution  of  formalin  than 
that  mentioned  tends  to  render  the  muscles  and  other  organs 
hard  and  leathery. 

It  is  also  a  good  plan,  although  not  necessary  to  the  success 
of  the  dissection,  to  inject  the  arteries  of  the  animal  first  with 
a  five  per  cent  solution  of  formalin,  which  preserves  the  internal 
organs  and  hardens  the  brain,  and  then  with  a  red  injection 
mass,  in  order  to  make  the  arteries  easier  to  study.  It  is  best 
to  do  this  through  the  femoral  artery  near  the  base  of  the  hind 
leg.  The  veins  can  also  be  injected,  if  desired,  at  the  same 
time,  with  a  blue  injection  mass  through  the  femoral  vein ; 
the  veins,  however,  can  be  easily  studied  without  injection. 
Skin  the  inner  surface  of  the  leg  from  the  trunk  to  the  knee. 
The  femoral  artery  and  vein  will  be  seen  lying  alongside  of 
each  other  in  the  middle  of  the  thigh,  very  near  the  surface  ;  the 
vein  is  the  larger  of  the  two,  and  is  filled  with  blood,  while 
the  artery  is  a  pale  pink  in  color. 

213 


214  VERTEBKATE  ZOOLOGY 

If  this  be  not  done,  it  will  be  necessary,  in  order  that  the 
brain  may  be  studied  when  the  time  comes,  to  cut  off  the  head 
of  a  fresh  cat  and,  after  sawing  off  the  top  of  the  skull,  to  place 
it  in  a  five  per  cent  solution  of  formalin,  or,  what  is  better,  a 
solution  consisting  of  one  part  of  five  per  cent  formalin  and  three 
parts  ninety-five  per  cent  alcohol,  and  to  leave  it  there  until  the 
brain  is  thoroughly  hardened  and  is  needed  for  study.  In  remov- 
ing the  top  of  the  skull,  care  must  be  taken  not  to  saw  into  the 
brain,  and  also  to  remove  the  transverse,  bony  partition  between 
the  cerebrum  and  the  cerebellum  without  injuring  either. 

Study  the  external  characters  of  the  animal.  Just  as  a  bird 
may  be  told  by  its  feathers,  so  the  most  distinguishing  feature 
of  the  mammal  is  its  hair;  all  mammals  have  hair,  and  only 
mammals  have  it.  It  is  a  highly  specialized  epidermal  struc- 
ture, whose  principal  function  is  the  retention  of  the  bodily 
heat  of  'the  animal.  The  warm  air  between  the  hairs  is  not 
easily  removed;  radiation  is  thus  checked  and  the  animal 
keeps  warm.  It  is  largely  due  to  the  development  of  hair 
that  mammals  have  become  animals  with  a  constant  temper- 
ature, or  warm-blooded  animals.  In  cold-blooded  animals  the 
temperature  is  in  a  high  degree  inconstant,  varying  sometimes 
100°  Fahr.  at  different  times,  —  being  approximately  that  of  the 
surrounding  air  or  water. 

Observe  the  arrangement  of  the  hair  on  the  body.  Almost 
the  entire  body  is  covered,  only  the  tip  of  the  nose,  the  walking 
pads  of  the  feet,  and  the  tips  of  the  nipples  being  bare.  Note 
the  difference  in  the  texture  of  the  hair  on  different  parts  of 
the  body.  The  most  highly  specialized  hairs  are  the  whiskers, 
or  vibrissae,  on  the  upper  lip,  the  sides  of  the  cheeks,  and  above 
the  eyes.  These  are  tactile  organs  and  are  an  important  assist- 
ance to  a  nocturnal  animal. 

Observe  the  color  of  the  animal  and  note  if  the  color  patches 
are  bilaterally  symmetrical.  The  domestic  cat  is  probably  de- 
scended from  the  Egyptian  wild-cat,  Felis  maniculata,  the  color 
of  which  is  mottled  gray,  very  much  like  that  which  is  so  com- 
mon among  domestic  cats ;  domestication,  however,  has  resulted 
in  a  wide  range  of  variation  in  color,  from  pure  white  to  pure 


THE  CAT  215 

black.  Observe  the  difference  in  color  between  different  regions 
of  the  animal's  body,  —  the  back  and  the  belly,  the  head  and 
the  trunk,  the  inner  and  the  outer  sides  of  the  leg,  etc. 

Observe  the  general  form  and  shape  of  the  body.  The  trunk 
is  a  laterally  compressed,  cylindrical  structure ;  the  head  is  large 
and  compact,  -the  neck  short,  and  the  tail  long.  The  rather 
short  legs  with  their  sharp  retractile  claws,  the  lithe,  muscular 
body,  the  strong  jaws  and  large  teeth  fit  the  animal  for  a  preda- 
ceous  life  in  the  woods  and  fields. 

The  body  may  be  divided  into  four  regions,  —  the  head,  neck, 
trunk,  and  tail ;  the  trunk  may  be  further  divided  into  the  tho- 
racic, lumbar,  and  sacral  subregions. 

The  head.  This  body  region  articulates  with  the  vertebral 
column  by  two  occipital  condyles.  It  is  very  solid  and  compact, 
all  of  the  bones  being  closely  knit  together,  and  the  upper  jaw 
being  firmly  joined  with  the  cranium.  This  feature  is  correlated 
with  the  structure  of  the  teeth.  Instead  of  these  being  all  alike  in 
form,  as  is  the  case  among  most  of  the  lower  vertebrates,  and 
being  of  use  principally  in  seizing  the  food,  they  are  specialized 
to  perform  a  variety  of  functions,  the  front  teeth  to  seize  the 
food  and  the  back  teeth  to  chew  it. 

The  mouth  is  large  and  is  guarded  by  upper  and  lower  lips. 
The  nostrils  are  a  pair  of  large  openings  at  the  end  of  the  project- 
ing nose.  The  eyes  are  large,  and  each  is  protected  by  three  eye- 
lids, —  the  upper  lid,  the  lower  lid,  and  the  nictitating  membrane,  or 
third  eyelid.  This  third  lid  is  an  opaque  membrane  at  the  inner 
corner  of  the  eye,  which  moves  across  it.  Take  hold  of  it  with 
forceps  and  pull  it  across  the  eye.  There  are  no  eyelashes,  the 
whole  surface  of  the  lids  being  covered  with  hair.  A  pair  of 
large  external  ears  is  present. 

The  neck.  The  neck  is  short  and  strong.  In  land  mammals 
the  length  of  the  neck  is  usually  correlated  with  the  length  of 
the  fore  legs ; — an  animal  with  long  legs  has  a  long  neck.  This 
is  because  the  mouth  is  the  usual  organ  of  prehension  and  the 
animals  seize  their  food  on  or  near  the  ground.  The  length  of 
the  neck  and  head  must  be  such  that  the  mouth  is  brought  to 
the  ground  when  the  head  is  bent  down. 


216  VEKTEBEATE  ZOOLOGY 

The  neck  in  all  land  vertebrates  is  a  flexible  body  division, 
its  principal  function  being  to  give  the  head  a  wide  range  of 
movement ;  this  is  important,  inasmuch  as  the  head  bears,  besides 
the  organs  of  prehension,  the  special  sense  organs,  which  are  the 
principal  organs  of  orientation. 

The  trunk.  This  region  is  made  up  of  the  thoracic,  lumbar, 
and  sacral  subregions,  —  the  first  and  third  of  which  are  rigid 
regions  and  support  the  two  pairs  of  extremities,  while  the 
second  is  a  flexible  one. 

The  thoracic  subregion  is  the  animal's  chest;  it  contains  the 
heart  and  lungs,  which  are  inclosed  in  a  bony  case  composed 
of  the  spinal  column,  the  ribs,  and  the  breastbone.  It  also  con- 
tains the  pectoral  girdle,  by  means  of  which  the  skeleton  of  the 
fore  limbs  is  joined  with  the  trunk.  This  girdle  consists  prin- 
cipally of  the  two  large  shoulder  blades  or  scapulae,  which  are 
imbedded  in  the  muscles  of  the  back  and  sides.  Two  pairs  of 
nipples  are  present  on  the  ventral  side  of  this  region. 

The  lumbar  subregion  is  the  animal's  abdomen  ;  it  contains  the 
bulk  of  the  important  viscera.  Its  walls  are  strengthened  dor- 
sally  by  the  spinal  column,  the  transverse  processes  of  which 
are  here  very  long ;  laterally  and  ventrally  they  have  no  bony 
support.  This  subregion  forms  the  pivot  of  the  body;  it  is 
where  the  body  bends  when  the  direction  of  movement  is 
changed.  It  follows,  consequently,  that  an  active  and  agile 
animal  like  the  cat  has  a  relatively  large  lumbar  region.  In  a 
two-legged  vertebrate,  like  the  bird,  the  body  does  not  bend 
when  the  direction  of  movement  is  changed,  and  the  lumbar 
region  is  not  functional  in  this  way.  Three  pairs  of  nipples  are 
present  on  the  ventral  side  of  this  region  in  the  cat. 

The  sacral  subregion  is  the  most  rigid  portion  of  the  body 
except  the  head.  In  it  lie  the  hinder  portions  of  the  digestive 
and  urogenital  organs,  together  with  the  anus  and  the  urogen- 
ital  openings,  the  former  of  which  is  dorsal  to- the  latter.  It  also 
contains  the  pelvic  girdle,  by  means  of  which  the  skeleton  of 
the  hind  limbs  is  joined  with  the  trunk.  The  forward  motion 
of  the  animal  is  accomplished  largely  by  means  of  the  hind 
limbs,  the  front  limbs  being  of  use  principally  in  supporting 


THE  CAT  217 

the  anterior  end  of  the  body  and  in  changing  the  direction  of 
movement.  The  connection  of  the  pelvic  girdle  with  the  trunk 
is  consequently  much  firmer  than  that  of  the  pectoral  girdle. 
The  pelvic  girdle  forms  a  complete  arch,  the  bones  of  which 
are  immovably  joined  with  one  another  and  also  with  the  spinal 
column  by  sutures. 

The  tail.  The  caudal  region  is  the  most  flexible  of  all.  It  is 
also  of  the  least  apparent  importance  to  the  animal,  and  varies 
much  in  size  in  different  cats.  In  Manx  cats  it  may  be  entirely 
absent;  in  Angora  cats  it  is  very  long  and  bushy.  In  water 
vertebrates  the  tail  is  a  very  important  part  of  the  body,  since 
it  is  the  principal  organ  of  locomotion.  Land  vertebrates  have 
inherited  it  from  their  aquatic  ancestors,  and  as  it  is  no  longer 
needed  for  locomotion  it  is  put  to  a  variety  of  uses,  —  and  may 
even  be  absent  altogether. 

The  appendages.  Two  pairs  of  appendages  are  present,  —  the 
fore  and  hind  limbs.  Each  is  made  up  of  three  divisions,  a  prox- 
imal, a  middle,  and  a  distal  division.  In  the  fore  limb  these  are  the 
upper  arm,  the  forearm,  and  the  wrist  and  hand  respectively. 
The  hand  'has  five  digits,  which  are  provided  with  retract- 
ile claws.  The  first  digit,  or  thumb,  is  above  the  others  and  is 
more  or  less  rudimentary.  Note  the  walking  pads  on  the  sole 
of  the  foot ;  on  the  opposite  side  to  the  thumb  is  a  small  pad 
which  is  over  the  pisiform  bone  of  the  wrist.  Identify  the  three 
divisions  of  the  leg,  —  also  the  shoulder  joint  and  the  elbow. 

In  the  hind  limb  the  proximal  division  is  the  thigh,  the  mid- 
dle division  is  the  shank,  and  the  distal  division  is  the  ankle 
and  foot,  the  latter  having  four  digits  which  are  provided  with 
retractile  claws.  Note  the  walking  pads  on  the  foot ;  also  the 
heel,  which  projects  back  from  the  upper  end  of  the  ankle. 
Identify  the  three  divisions  of  the  leg ;  also  the  hip  joint  and 
the  knee. 

Observe  the  position  of  the  fore  and  hind  legs  with  reference 
to  the  trunk  and  to  each  other.  The  elbow  and  the  knee  will 
be  seen  to  project  in  opposite  directions,  the  elbow  being  directed 
backward  and  the  knee  forward.  The  primitive  positions  of  the 
vertebrate  leg,  as  illustrated  in  some  of  the  lower  amphibians, 


218  VERTEBRATE  ZOOLOGY 

have  already  been  spoken  of  (see  page  67).  In  most  of  the 
land  vertebrates  a  further  important  change  in  the  position  of 
the  limbs  takes  place,  which  consists  in  the  rotation  of  the  whole 
limb  about  90°.  The  fore  limb  rotates  backward  and  the  hind 
limb  forward,  so  that  the  elbow  and  the  knee  come  to  point 
toward  each  other  instead  of  in  the  same  direction. 

In  the  hind  limb  the  preaxial  or  anterior  side,  on  which  is 
the  big  toe,  is  turned  inward  toward  the  body  by  this  move- 
ment, and  the  foot  comes  to  be  directed  forward. 

The  fore  limb,  in  the  cat  and  in  most  other  mammals,  under- 
goes a  further  change.  The  preaxial  side  of  it  with  the  thumb,  by 
the  rotation  just  mentioned,  would  be  turned  outward,  away 
from  the  body ;  and  the  fore  foot,  as  well  as  the  proximal  divi- 
sion of  the  leg,  would  be  directed  backward.  The  lower  end  of 
the  preaxial  side,  however,  rotates  again  around  to  the  inner  side 
of  the  leg,  so  that  in  its  final  position  it  is  on  the  side  toward 
the  body  and  the  foot  is  directed  forward. 

It  is  in  this  way  that  the  big  toe  and  the  thumb  both  come  to 
be  on  the  side  of  the  leg  toward  the  body,  and  both  feet  to  be 
directed  forward,  notwithstanding  the  fact  that  the  knee  and 
the  elbow  are  directed  in  opposite  directions. 

Exercise  1.  Draw  an  outline  of  a  side  view  of  the  cat,  and  label 
the  various  parts  of  the  body. 

Exercise  2.  Draw  a  dorsal  view  of  the  head. 

Exercise  3.  Draw  a  front  view  of  the  head,  showing  the  nostrils 
and  mouth. 

Exercise  4.  Draw  a  semidiagrammatic  sketch  of  the  inner  surface 
of  the  fore  foot  and  the  hind  foot,  showing  the  toes,  claws, 
and  walking  pads.  Label  all. 

The  internal  organs.  Place  the  animal  on  its  back  on  a  dis- 
secting board  and  fasten  each  foot  firmly  to  the  board  by  means 
of  a  nail  or  strong  pin,  or  a  cord.  Make  an  incision  through 
the  skin  in  the  mid  ventral  line  the  entire  length  of  the  body. 
Separate  the  skin  from  the  fat  and  muscles  beneath  it  for  a  short 


THE  CAT  219 

distance  on  each  side  of  the  incision ;  if  the  animal  is  very  fat, 
remove  the  fat  present  here.  Make,  now,  a  midventral  incision 
through  the  body  wall  from  the  pelvic  girdle,  which  may  be  felt 
through  the  muscles  at  the  hinder  end  of  the  trunk,  to  the 
breastbone,  which  may  also  be  felt  a  short  distance  back  of  the 
fore  legs ;  make  also  a  short  transverse  cut  from  the  middle  of 
this  incision  on  each  side. 

The  cavity  of  the  abdomen  will  thus  be  opened.  The  red 
lobes  of  the  liver  with  the  green  gall  bladder,  and  the  stomach  will 
be  seen  at  the  forward  end  of  this  cavity,  the  latter  organ  lying 
at  the  left  of  the  liver.  Back  of  them  is  an  extensive  mem- 
brane, the  fat-filled  great  omentum,  covering  the  intestine.  At 
the  hinder  end  of  the  cavity  will  be  seen  the  urinary  bladder, 
which  is  joined  with  the  ventral  body  wall  by  a  thin  mesentery. 
The  forward  ends  of  the  stomach  and  liver  rest  against  a  trans- 
verse muscular  partition,  —  the  diaphragm,  —  which  forms  the 
forward  wall  of  the  abdominal  cavity. 

Make  now  with  scissors  a  longitudinal  incision  along  each 
side  of  the  breastbone  through  the  body  wall  to  the  forward 
end  of  the  trunk.  Cut  the  diaphragm  where  it  joins  the  ven- 
tral body  wall  on  each  side.  Lift  up  the  hinder  end  of  the 
breastbone  and,  without  further  cutting  or  disturbing  anything, 
look  into  the  thoracic  cavity,  which  is  thus  opened. 

It  will  be  seen,  in  the  first  place,  that  the  entire  body  cavity 
is  made  up  of  these  two  divisions,  —  the  abdominal  cavity  and  the 
thoracic  cavity,  —  which  are  separated  by  the  diaphragm. 

The  thoracic  cavity  contains  the  lungs,  the  heart  and  the  great 
vessels  which  enter  and  leave  it,  the  posterior  portion  of  the 
ffisophagus  and  the  trachea,  and  the  thymus.  A  thin  membrane 
called  the  pleura  lines  its  inner  surface.  The  space  within  the 
thorax  is  not,  however,  a  continuous  one,  but  is  subdivided 
into  several  distinct  compartments.  The  pleura  forms  two 
closed  sacs,  called  the  pleural  sacs,  which  occupy  the  right  and 
left  sides  of  the  thoracic  cavity.  Within  each  of  these  sacs  one 
of  the  lungs  projects,  covered  by  a  fold  of  the  pleura. 

The  medial  walls  of  the  pleural  sacs  do  not  extend  to  the 
median  plane  of  the  body,  but  inclose  between  themselves  a 


220  VERTEBRATE   ZOOLOGY 

large  space  called  the  mediastinum,  which  occupies  the  medial 
area  of  the  thoracic  cavity.  Within  this  space  lie  the  median, 
unpaired  organs  of  the  thorax,  —  the  heart  and  its  great  vessels, 
the  oesophagus,  the  trachea,  and  the  thymus. 

By  lifting  up  the  hinder  end  of  the  breastbone  a  view  of  the 
thoracic  cavity  will  be  obtained.  The  large  heart  will  be  seen 
inclosed  in  the  membranous  pericardium,  in  which  much  fat  is 
often  imbedded.  Dorsal  to  the  heart  are  two  thin  membranes 
passing  diagonally  to  the  right  and  left,  to  the  dorsal  body 
wall.  These  are  the  medial  walls  of  the  pleural  sacs,  and  the 
space  between  them  is  the  mediastinum,  in  which  the  heart  lies. 
Ventral  to  the  heart  the  walls  of  the  mediastinum  are  much 
nearer  together  than  dorsally,  and  appear  as  a  single  membrane 
which  joins  the  pericardium  with  the  body  wall  in  the  midven- 
tral  plane.  Do  not  disturb  any  of  these  organs. 

Exercise  5.  Draw  a  figure  representing  a  diagrammatic  cross 
section  through  the  thoracic  cavity,  showing  the  relative 
positions  of  the  two  pleural  sacs,  the  mediastinum,  the 
pericardium,  and  the  lungs. 

The  abdominal  cavity  contains  the  greater  part  of  the  digestive 
organs,  the  reproductive  organs,  and  other  important  viscera. 
It  is  lined  by  a  thin  membrane  called  the  peritoneum,  which 
forms  a  sac  inclosing  nearly  the  entire  abdominal  space.  Just 
as  the  pleural  sacs  are  closed  sacs,  so  the  peritoneal  sac,  in  the 
male  animal,  is  a  closed  one,  while  in  the  female  it  is  closed 
except  that  the  reproductive  system  furnishes  a  pair  of  open- 
ings to  the  exterior  through  which  ova  and  young  find  an  exit. 
Also,  just  as  the  lungs  and  other  organs  project  into  the  pleural 
sacs,  covered,  however,  by  folds  of  their  walls,  so  the  various 
organs  of  the  abdominal  cavity  project  into  it,  carrying  folds 
of  the  peritoneal  wall  with  them.  Thus  all  of  the  abdominal 
organs  will  be  found  attached  to  the  abdominal  wall  by  these 
peritoneal  folds,  which  are  called  mesenteries,  in  the  broad  use 
of  the  term. 

Immediately  back  of  the  diaphragm  are  the  stomach  and  the 
liver,  as  we  have  already  seen.  The  mesentery  of  the  latter  is 


THE  CAT  221 

called  the  suspensory  ligament;  it  is  the  median,  vertical  mem- 
brane, which  appears  between  the  right  and  the  left  halves  of 
the  liver  and  joins  it  with  the  diaphragm.  Appearing  on  the 
right  side  of  the  liver  is  the  green  gall  bladder.  The  great 
omentum,  which  covers  the  viscera  back  of  the  liver,  is  the 
mesentery  of  the  stomach.  It  arises  from  the  peritoneum  in 
the  middorsal  line  between  the  diaphragm  and  the  kidneys, 
and,  instead  of  passing  directly  to  the  stomach,  goes  first  pos- 
teriorly to  the  region  of  the  pelvis,  and  then,  turning  on  itself, 
passes  forward  to  the  greater  curvature  of  the  stomach.  Thus 
it  will  be  seen  to  form  a  great  sac,  the  omental  sac,  which  lies 
ventral  to  almost  the  entire  abdominal  viscera. 

The  abdominal  cavity  in  mammals  is  not  the  equivalent  of 
the  entire  abdominal  cavity  of  other  vertebrates,  but  only  of  the 
middle  and  hinder  portions  of  it.  In  other  vertebrates  no  dia- 
phragm and  consequently  no  thoracic  cavity  is  present,  the  body 
cavity  being  divided  into  the  abdominal  and  pericardial  cavities. 
In  mammals  the  pericardial  cavity  with  the  heart  is  contained 
in  the  thoracic  cavity. 

Exercise  6.  Draw  a  semidiagrammatic  sketch  of  the  abdominal 
cavity,  in  an  outline  of  the  body,  together  with  the  organs 
which  appear  in  a  ventral  view.  Carefully  label  all  of 
them. 

The  digestive  system.  This  is  made  up  of  the  mouth,  pharynx, 
oesophagus,  stomach,  small  intestine,  large  intestine,  the  sali- 
vary glands,  liver,  and  pancreas.  Lift  up  the  great  omentum 
and  cut  it  away,  being  careful  not  to  injure  the  viscera  with 
which  it  is  joined.  The  flat  dark-red  spleen  will  be  seen  in  the 
omentum  on  the  left  side  of  the  body  close  to  the  stomach, 
also  the  large  splenic  veins  and  arteries.  Close  to  the  dorsal  sur- 
face of  the  stomach  and  in  contact  with  the  spleen  is  a  portion 
of  the  long,  flat,  light-red  pancreas.  Do  not  cut  or  remove  any 
of  these  organs. 

The  stomach  and  intestine  are  thus  fully  exposed.  Observe 
carefully  the  form  and  position  of  the  stomach.  Note  where  the 
oesophagus  comes  through  the  diaphragm  and  joins  it.  The 


222  VERTEBRATE  ZOOLOGY 

stomach  has  two  distinct  divisions,  —  the  broad  anterior  portion 
which  lies  directly  back  of  the  diaphragm  on  the  left  side  of 
the  body,  and  the  narrow  posterior  portion  which  bends  sharply 
forward  and  lies  near  the  median  plane.  Its  anterior  end, 
where  the  oesophagus  joins  it,  is  called  the  cardiac  end;  the  pos- 
terior end,  where  it  passes  into  the  intestine,  is  called  the  pyloric 
end.  Its  convex  left  side  is  called  the  greater  curvature,  and  the 
concave  right  side,  the  lesser  curvature.  The  portion  of  the  greater 
curvature  which  extends  farthest  to  the  left  is  called  the  fun- 
dus  of  the  stomach. 

Study  the  course  of  the  intestine.  This  portion  of  the  diges- 
tive tract  is  made  up  of  two  divisions,  —  an  anterior  division, 
the  small  intestine,  and  a  posterior  division,  the  large  intestine. 

The  small  intestine  is  further  divided  into  three  parts,  —  the 
duodenum,  the  jejunum,  and  the  ileum.  The  duodenum  is  that 
portion  immediately  posterior  to  the  stomach.  Note  the  sharp 
turn  it  makes  as  it  leaves  the  pyloric  end  of  that  organ.  It  is 
five  or  six  inches  in  length  and  U-shaped,  and  between  its  two 
limbs  lies  a  portion  of  the  light-red  pancreas.  Turn  the  intes- 
tine to  the  left  and  the  course  of  the  duodenum  will  be  seen. 
No  definite  boundary  separates  the  duodenum  from  the  jejunum  ; 
this  division  and  the  ileum  each  forms  about  half  the  remaining 
part  of  the  small  intestine.  Lift  them  up  and  note  the  mesen- 
tery which  joins  them  with  the  dorsal  body  wall,  but  do  not 
cut  it.  The  hinder  end  of  the  ileum  will  be  seen  to  lie  on  the 
right  side  of  the  body,  where  it  joins  the  large  intestine. 

The  large  intestine  is  divided  into  the  colon  and  the  rectum. 
The  colon,  the  anterior  division,  is  a  thick  tube  which  lies  back 
of  the  liver  and  stomach  against  the  dorsal  body  wall.  The 
ileum  does  not  join  the  colon  at  the  anterior  end  of  the  latter, 
but  a  short  distance  from  it,  and  the  blind  sac  thus  formed  is 
called  the  caecum.  This  pouch  is  a  rudiment  of  a  division  of 
the  intestine,  which  in  many  vegetarian  animals,  as  the  rabbit, 
is  very  long ;  in  man  the  hinder  portion  of  it  is  the  vermiform 
appendix.  The  colon  may  be  divided  into  three  parts,  —  the 
ascending  colon,  the  short  anterior  portion  which  lies  on  the  right 
side  of  the  animal  and  extends  forward ;  the  transverse  colon, 


THE  CAT  223 

which  extends  transversely  to  the  left ;  and  the  descending  colon, 
which  extends  back  to  the  rectum.  This  last-named  portion  of 
the  large  intestine  extends  along  the  middorsal  line  of  the  body 
cavity  to  the  anus.  Its  anterior  end  is  not  sharply  separated 
from  the  colon ;  its  posterior  end  is  constricted.  Note  the  mes- 
entery which  joins  the  large  intestine  with  the  dorsal  body  wall, 
but  do  not  cut  it. 

In  order  to  study  the  hinder  end  of  the  rectum,  the  pelvis 
must  be  split  in  the  midventral  line,  which  is  easily  accom- 
plished with  a  scalpel  by  cutting  the  midventral  suture.  Grasp 
one  of  the  legs  firmly  in  each  hand  and  bend  them  sharply  back, 
thus  making  a  space  an  inch  or  more  in  width  between  the 
two  halves  of  the  pelvis  and  exposing  the  rectum. 

Exercise  7-  Draw  a  sketch  of  the  abdominal  cavity  with  the 
great  omen  turn  removed,  showing  the  natural  position  of 
the  organs  exposed.  Carefully  label  all. 

Study  the  forrA  and  position  of  the  liver  and  pancreas,  but 
without  cutting  them  or  any  of  their  connections.  The  liver  is 
divided  into  two  main  lobes,  —  the  right  and  the  left  lobe,  between 
which  is  the  suspensory  ligament.  Note  carefully  the  minor  lobes 
into  which  each  of  these  lobes  is  divided.  Turn  the  hinder  end 
of  the  liver  forward  and  pin  it  there,  and  observe  its  dorsal  and 
posterior  surfaces.  Note  carefully  the  lobes  which  appear  in 
this  view.  The  gall  bladder  will  be  seen  in  the  right  lobe. 

Turn  the  entire  intestine  as  far  as  possible  to  the  animal's 
left  without  cutting  the  mesentery,  and  fasten  it  there.  The 
dorsal  wall  of  the  abdominal  cavity  will  thus  be  exposed.  Note 
the  large  right  kidney  on  the  right  side,  just  back  of  the  liver, 
usually  imbedded  in  fat.  Two  large  veins  will  be  seen,  the  larger 
of  the  two,  and  the  largest  vein  in  the  body,  being  the  postcaval. 
This  vein  lies  in  the  median  plane  near  the  dorsal  body  wall, 
between  the  two  kidneys,  from  each  of  which  a  prominent  renal 
vein  will  be  seen  going  to  it.  It  passes  forward  into  one  of  the 
divisions  of  the  right  lobe  of  the  liver,  on  its  way  to  the  heart. 
The  other  vein  is  the  superior  mesenteric  vein  and  its  forward  con- 
tinuation, the  portal  vein.  The  superior  mesenteric  lies  in  the 


224  VERTEBRATE  ZOOLOGY 

mesentery,  in  the  loop  of  the  duodenum,  alongside  the  pancreas  ; 
the  portal  lies  in  front  of  the  loop  and  passes  to  the  dorsal  sur- 
face of  the  liver,  where  it  breaks  up  into  a  number  of  branches 
which  enter  the  various  lobes. 

Lying  alongside  these  branches  of  the  portal  vein  are  the 
much  smaller  bile  ducts,  which  collect  bile  from  the  lobes  of  the 
liver.  A  duct  from  the  gall  bladder,  called  the  cystic  duct,  joins 
these  bile  ducts,  and  the  union  of  all  of  these  forms  the  common 
bile  duct,  which  lies  alongside  the  portal  vein  and  carries  the 
bile  to  the  duodenum.  Trace  these  ducts  ;  if  they  are  not  easily 
seen,  they  may  often  be  made  apparent  by  squeezing  bile  into 
them  from  the  gall  bladder. 

The  pancreas  is  a  long,  flat  gland  four  or  five  inches  in  length. 
It  has  two  limbs  which  lie  at  right  angles  to  each  other.  One 
of  these  lies  in  the  loop  of  the  duodenum ;  the  other  extends  to 
the  left  side  of  the  body  cavity  along  the  dorsal  surface  of  the 
stomach.  The  pancreas  communicates  with  the  duodenum  usu- 
ally by  two  ducts.  The  pancreatic  duct  lies  near  the  bend  of  the 
pancreas,  joins  the  common  bile  duct,  and  enters  the  duodenum 
with  it ;  the  accessory  pancreatic  duct,  which  is  sometimes  wanting, 
enters  the  duodenum  about  an  inch  back  of  it. 

A  number  of  large,  soft  lymph  glands  are  present  in  the  mes- 
entery, the  largest  of  which  is  about  two  inches  in  length  and 
situated  near  the  center  of  the  mesentery;  it  is  called  the 
pancreas  Aselli,  but  is  not  a  pancreas. 

Exercise  8.  Make  a  semidiagrammatic  sketch  showing  the  dorsal 
and  posterior  surfaces  of  the  liver,  the  pancreas,  and  the 
duodenum,  the  bile  and  pancreatic  ducts,  and  the  branches 
of  the  portal  vein  on  the  surface  of  the  liver,  so  far  as 
observed. 

The  study  of  the  digestive  tract  will  be  finished  after  that 
of  the  portal  veins. 

The  vascular  system.  This  is  composed  of  the  following 
organs :  (1)  the  heart,  (2)  the  arteries,  (3)  the  veins,  (4)  the 
capillaries,  and  (5)  the  lymph  vessels.  The  heart  is  a  muscular 
pump  containing  two  auricles  and  two  ventricles ;  it  drives  the 


THE  CAT  225 

blood  through  two  systems  of  arteries,  —  (a)  the  pulmonary  arteries, 
which  take  venous  blood  from  the  right  ventricle  to  the  lungs 
to  be  aerated,  and  (b)  the  systemic  arteries,  which  take  arterial 
blood  from  the  left  ventricle  to  the  various  tissues  and  organs 
of  the  body.  The  heart  receives  blood  through  two  systems  of 
veins,  —  (a)  the  pulmonary  veins,  which  bring  arterial  blood  from 
the  lungs  to  the  left  auricle,  and  (b)  the  systemic  veins,  which 
bring  venous  blood  from  the  tissues  and  organs  of  the  body 
to  the  right  auricle. 

The  systemic  veins  may  be  further  subdivided  into  two  sys- 
tems, —  (a)  the  caval  system,  by  which  the  blood  is  brought  directly 
to  the  heart,  and  (b)  the  portal  system,  by  which  the  blood  is  taken 
from  the  digestive  tract  and  spleen  directly  to  the  liver,  from 
which  organ  it  goes  to  the  heart  through  the  hepatic  veins. 

The  portal  system.  This  system  consists  of  the  portal  vein 
and  several  smaller  veins  which  meet  to  form  it.  The  portal  vein 
and  the  superior  or  anterior  mesenteric,  the  largest  of  its  tributaries, 
have  just  been  observed.  The  latter  joins  the  former  near  the 
pyloric  end  of  the  stomach,  bringing  blood  from  the  intestine. 
Observe,  without  cutting  the  mesentery,  the  mesenteric  veins 
which  radiate  to  the  superior  mesenteric  from  every  part  of 
the  small  intestine.  A  single  large  branch  of  the  latter  vein 
called  the  inferior  or  posterior  mesenteric  brings  blood  from  the 
large  intestine.  The  gastrosplenic  vein  joins  the  portal  near  the 
base  of  the  superior  mesenteric ;  it  is  formed  by  the  union  of 
branches  from  the  spleen,  stomach,  pancreas,  and  great  omentum. 
Besides  these  veins  the  portal  also  receives  a  number  of  smaller 
veins  from  the  duodenum,  pancreas,  and  the  stomach. 

Study  all  of  these  veins,  but  without  cutting  the  mesentery 
in  which  they  lie.  Note  also  that  alongside  the  mesenteric 
veins  lie  the  mesenteric  arteries.  These  arteries  are  somewhat 
smaller  than  the  veins  which  accompany  them  and  are  a  light 
pink  in  color,  while  the  veins  are  dark-colored. 

Exercise  9.  Draw  a  diagram  showing  the  portal  system. 

The  digestive  system  (continued).  Lift  up  the  intestine  and 
cut  the  mesentery  where  it  joins  it ;  cut  also  the  bile  and  the 


226  VERTEBRATE  ZOOLOGY 

pancreatic  ducts.  Straighten  out  the  intestine  from  the  stomach 
to  the  anus.  Be  careful,  however,  not  to  injure  the  bladder, 
which  lies  ventral  to  the  rectum.  The  two  ureters,  also,  which 
join  the  bladder  with  the  kidneys  and  appear  as  white  cords, 
and  in  the  male  the  vasa  deferentia,  which  also  appear  as  white 
cords  lying  ventral  to  the  rectum,  must  be  carefully  preserved. 
Find  the  anterior  or  cardiac  end  of  the  stomach  and  note  the 
oesophagus  which  comes  through  the  diaphragm  from  the  tho- 
racic cavity  and  joins  it.  With  scissors  cut  the  oesophagus ; 
cut  the  connections  of  the  stomach  and  take  it  and  the  intestine 
from  the  body. 

Exercise  10.  Draw  an  outline  of  the  stomach  and  duodenum, 
the  hinder  part  of  the  ileum,  and  the  large  intestine.  Label 
all  carefully. 

Cut  the  rectum  at  the  level  of  the  bladder,  taking  care  not 
to  injure  the  ureters  and,  in  the  male,  the  vasa  deferentia.  Slit 
open  the  stomach  and  note  the  longitudinal  folds  of  its  mucous 
membrane;  at  its  pyloric  end  note  the  pyloric  valve,  a  constric- 
tion caused  by  the  thickening  of  the  circular  muscles  of  the 
stomach  at  this  point.  Slit  open  the  duodenum  and  note  its 
velvety  appearance,  which  is  caused  by  the  presence  of  the  villi, 
delicate  fingerlike  projections  of  the  mucous  membrane.  Slit 
open  the  hinder  end  of  the  ileum,  together  with  the  caecum  and 
the  forward  portion  of  the  colon,  and  note  the  ileocolic  valve,  a 
projection  of  the  inner  wall  of  the  ileum  into  the  colon  which 
permits  substances  to  pass  in  one  direction  only. 

Exercise  11.  Make  a  drawing  showing  the  ileocolic  valve. 

The  urogenital  system.  This  system  includes  the  urinary 
and  the  genital  organs.  Although  these  two  groups  of  organs 
are  quite  different  in  function  they  bear  a  close  topographical 
relation  to  each  other  and  will  be  studied  together. 

The  urinary  system  consists  of  a  pair  of  kidneys,  a  pair  of 
ureters,  a  urinary  bladder,  and  a  urethra.  The  kidneys  are  large, 
reniform  bodies,  which  lie  against  the  dorsal  body  wall  on  either 
side  of  the  spinal  column  in  the  middle  of  the  abdominal  cavity ; 


THE  CAT  227 

the  right  kidney  lies  somewhat  in  advance  of  the  left  one.  The 
peritoneum  stretches  over  the  ventral  surface  of  the  kidney  and 
holds  it  tightly  against  the  muscles  of  the  body  wall,  and  around 
its  sides  between  the  peritoneum  and  the  muscles  is  a  great 
accumulation  of  fat.  On  the  medial  side  of  the  kidney  is  the 
slight  concavity  called  the  hilus,  where  the  ureter  and  renal  vein 
leave  it  and  the  renal  artery  enters  it.  The  artery  enters  the 
body  of  the  kidney ;  the  branches  of  the  vein  will  be  seen  on 
its  outer  surface. 

The  ureter  is  a  long  tube  which  passes  along  the  dorsal  body 
wall  on  one  side  of  the  vertebral  column  from  the  kidney  to 
the  dorsal  surface  of  the  neck  of  the  bladder.  It  has  the  appear- 
ance of  a  white  cord  and  is  often  imbedded  in  fat.  Its  anterior 
end  is  called  the  pelvis;  this  is  a  funnel-shaped  sac,  the  large 
end  of  which  is  imbedded  in  the  kidney  and  catches  the  urine 
as  it  oozes  from  the  mouths  of  the  kidney  tubules,  while  its 
small  end  emerges  from  the  hilus  as  the  ureter  proper.  In  the 
male  animal  the  two  ureters,  near  their  hinder  ends,  pass  through 
the  loops  made  by  the  two  vasa  deferentia. 

Remove  the  fat  from  the  kidney  and  the  ureter  on  the  right  side 
of  the  animal ;  be  careful  not  to  cut  the  latter  or  any  of  the  veins 
or  arteries  near  it.  The  large  median  vein  between  the  kidneys 
is  the  postcaval  vein ;  the  large  median  artery  is  the  dorsal  aorta. 
The  renal  vein  and  the  renal  artery  on  each  side  will  also  be  seen. 

The  urinary  bladder  is  a  muscular,  pear-shaped  sac  which  lies 
in  the  hinder  part  of  the  abdominal  cavity  between  the  rectum 
and  the  ventral  body  wall.  Its  larger  end  is  directed  forward ; 
its  smaller  end,  the  neck,  receives  the  ureters,  and  is  directed 
backward.  In  the  male  animal  the  neck  is  continued  in  the 
form  of  the  urethra  or  urogenital  canal,  and  receives  the  vasa 
deferentia,  which  bring  spermatozoa  from  the  testes.  It  passes 
through  the  penis,  at  the  distal  end  of  which  is  the  external 
opening,  and  becomes  the  common  outlet  for  both  urinary  and 
genital  organs.  In  the  female  the  neck  of  the  bladder  opens  into 
the  urogenital  sinus  or  vestibule,  a  short,  wide  space  which  also 
receives  the  vagina  and  is  equivalent  to  the  urogenital  canal  of 
the  male  ;  it  opens  to  the  outside  through  the  vulva. 


228  VERTEBRATE   ZOOLOGY 

The  bladder  is  supported  by  three  mesenteries,  —  the  median, 
ventral  suspensory  ligament,  and  the  two  lateral  ligaments  which 
join  it  with  the  dorsal  body  wall. 

Exercise  12.  Draw  a  semidiagrammatic   sketch  of  the  urinary 
system. 

Remove  one  of  the  kidneys  from  the  body,  split  it  longitudi- 
nally, and  study  the  cut  surface.  The  kidney  will  be  seen  to 
be  made  up  of  a  light-colored  peripheral  layer,  which  is  called 
the  cortical  substance,  and  a  darker  central  mass  called  the  medul- 
lary substance.  The  kidney  tubules  will  be  seen  as  fine  lines 
which  converge  to  a  large  space  near  the  concave  side  called 
the  sinus.  It  contains  the  wide,  funnel-shaped  anterior  end  of 
the  ureter  which,  as  we  have  already  learned,  is  called  the 
pelvis.  The  opening  of  the  sinus  to  the  outside,  through  which 
the  ureter  emerges,  is  the  hilus. 

Exercise  13.  Make  a  drawing  of  the  cut  surface  of  the  kidney. 

The  suprarenal  or  adrenal  bodies  are  a  pair  of  ovoid  bodies  which 
lie  imbedded  in  fat  immediately  in  front  of  the  kidneys.  Their 
function  is  unknown. 

The  genital  organs  in  the  male  are  the  following  :  a  pair  of 
genital  glands  called  the  testes,  which  lie  in  an  integumental 
pouch  called  the  scrotal  sac,  situated  just  ventral  to  the  anus ; 
a  pair  of  efferent  canals,  through  which  the  spermatozoa  are 
conducted  away  from  the  testes  to  the  urogenital  canal ;  two 
sets  of  glands,  —  the  bilobed  prostate  gland  and  the  paired 
Cowper's  glands,  — which  furnish  the  fluid  in  which  the  sper- 
matozoa are  suspended ;  and  the  penis,  through  which  the  uro- 
genital canal  or  urethra  passes  to  the  external  opening  at  its 
distal  end. 

Each  efferent  canal  is  made  up  of  two  portions,  —  the  epididy- 
mis  and  the  vas  deferens.  The  vasa  deferentia  have  already  been 
seen.  Each  appears  as  a  long  white  cord  which  forms  a  loop 
around  the  ureter  and  enters  the  neck  of  the  bladder.  Follow 
one  of  them  to  the  bladder.  Follow  it  in  the  opposite  direction ; 
it  may  be  traced  back  to  the  muscular  wall  of  the  abdominal 


THE  CAT  229 

cavity,  through  which  it  passes  by  a  small  opening  called  the 
inguinal  canal,  and  finally  proceeds  to  the  testis.  Carefully  remove 
the  skin  from  the  scrotal  sac,  and  from  the  penis,  which  lies 
between  the  testes. 

•  The  scrotal  sac  will  be  seen  to  contain  two  compartments, 
in  each  of  which  lies  a  testis.  Expose  one  of  the  testes.  It  is 
a  compact  elliptical  body  composed  of  a  mass  of  tubules  which 
may  be  seen  through  the  outer  covering;  these  are  the  semi- 
niferous tubules  and  produce  the  spermatozoa.  The  testis  is 
closely  invested  by  a  fold  of  the  peritoneum,  which  here  forms 
a  very  deep,  narrow  pocket  extending  into  the  scrotum  from 
the  abdominal  cavity,  with  which  the  testis  is  joined  by  the 
spermatic  cord.  This  cord  is  made  up  of  the  slender  anterior 
portion  of  this  peritoneal  pocket,  and  the  vas  deferens,  sper- 
matic artery,  and  spermatic  vein,  which  give  the  cord  its  solid 
appearance ;  they  form  the  connection  between  the  testis  arid 
the  organs  of  the  abdominal  cavity.  When  we  remember  that 
the  testes  have  migrated  from  their  original  position  near  the 
kidneys,  through  the  muscles  of  the  abdominal  wall  to  the 
scrotum,  carrying  the  vasa  deferentia  and  the  blood  vessels 
with  them,  we  can  understand  how  the  spermatic  cord  has 
come  into  existence. 

On  the  medial  surface  of  the  testis  and  at  its  two  ends  is  a 
white,  bandlike  mass  of  convoluted  tubes.  This  is  the  epididy- 
mis,  the  beginning  of  the  efferent  duct  of  the  testis.  It  is  com- 
posed of  three  parts,  —  the  caput  epididymis,  which  caps  the 
anterior  end  of  the  testis,  a  band  extending  from  the  caput 
along  its  inner  side  to  the  posterior  end,  and  the  cauda  epididymis, 
the  enlarged  posterior  end. 

The  caput  epididymis  is  joined  with  the  seminiferous  tubules 
of  the  testes  by  minute  vessels  called  the  vasa  efferentia.  The 
vas  deferens  begins  at  the  cauda  epididymis,  passes  forward  with 
many  convolutions  along  the  inner  side  of  the  testis,  and  finally, 
as  a  part  of  the  spermatic  cord,  passes  through  the  inguinal 
canal  into  the  abdominal  cavity  and  to  the  neck  of  the  bladder. 
Surrounding  the  ends  of  the  vasa  deferentia  is  the  bilobed  pros- 
tate gland.  About  an  inch  back  of  this  gland  are  the  paired 


230  VERTEBRATE   ZOOLOGY 

Cowper's  glands,  directly  back  of  which  the  urethra  enters  the 
penis.  This  structure  is  formed  of  three  elongated  cylindrical 
bodies,  —  the  median  ventral  corpus  spongiosum,  through  which 
the  urethra  runs,  and  the  two  lateral  corpora  cavernosa.  The 
latter  diverge  to  the  right  and  left  at  their  proximal  ends  and 
form  the  crura  penis.  The  distal  end  of  the  penis  is  formed 
by  the  greatly  enlarged  end  of  the  corpus  spongiosum  and  is 
called  the  glans  penis ;  a  fold  of  skin  called  the  prepuce  projects 
over  it.  A  small  bone  is  present  just  above  the  urethra,  near 
its  distal  end. 

The  female  genital  organs  are  the  following:  a  pair  of  genital 
glands  called  the  ovaries,  which  produce  the  ova;  a  pair  of 
efferent  ducts  which  receive  the  ova  and  in  which  the  young 
go  through  their  fetal  development ;  and  the  urogenital  sinus. 
Each  efferent  duct  is  composed  of  the  Fallopian  tube,  the  uterus, 
and  the  vagina. 

The  ovaries  are  small,  bean-shaped  bodies,  less  than  half  an 
inch  long,  which  lie  a  short  distance  back  of  the  kidneys,  near 
the  dorsal  body  wall.  Each  is  held  in  place  by  a  broad  mesen- 
tery, the  ligamentum  uteri,  which  passes  from  the  uterus  to  the 
dorsal  body  wall  and  holds  the  ovary  in  one  of  its  folds.  The 
narrow  ligamentum  ovarii  joins  it  with  the  ventral  body  wall. 
Examine  the  ovary  with  a  hand  lens  and  note  the  fine  white 
points  which  give  its  surface  a  granular  appearance ;  these  are 
the  Graafian  follicles,  in  each  of  which  is  an  ovum.  Corpora  lutea 
—  follicles  which  have  discharged  their  ova  —  may  also  be 
present  and  will  appear  as  red  elevations. 

The  anterior  end  of  the  efferent  duct  is  the  Fallopian  tube  or 
oviduct.  It  is  a  narrow,  convoluted  tube,  with  a  very  wide,  open 
anterior  end,  called  the  ostium,  the  fluted  edges  of  which  are 
partly  thrown  around  the  ovary  and  catch  the  ova  as  they 
emerge.  The  posterior  end  of  the  Fallopian  tube  is  continuous 
with  the  uterus. 

The  uterus  is  a  large,  Y-shaped  structure  ;  it  consists  of  a  pos- 
terior median  portion,  or  body,  and  an  anterior  paired  portion 
composed  of  two  horns,  which  extend  from  the  body  to  the 
Fallopian  tubes.  The  posterior  end 'of  the  uterus  projects  into 


THE  CAT  231 

the  vagina,  forming  the  cervix  uteri,  or  neck  of  the  uterus.  The 
uterus  is  attached  to  the  dorsal  body  wall  mainly  by  the  liga- 
mentum  uteri. 

The  vagina  extends  from  the  uterus  to  the  urogenital  sinus ; 
it  lies  beneath  the  rectum  and  just  above  the  neck  of  the 
bladder. 

The  urogenital  sinus  is  a  short,  wide  tube  which  opens  to  the 
outside  through  the  vulva,  immediately  beneath  the  anus.  The 
opening  of  the  bladder  into  it  is  ventral  to  that  of  the  vagina. 
Arising  from  the  floor  of  the  sinus,  just  beneath  the  former,  is  a 
slight  elevation,  the  clitoris,  which  is  homologous  to  the  penis 
of  the  male. 

Exercise  14.  Draw    a   semidiagrammatic    view   of    the    genital 
organs. 

The  vascular  system  (continued] ;  the  caval  veins.  We  shall 
now  begin  to  study  the  veins  which  carry  venous  blood  directly 
to  the  heart.  Three  groups  of  these  veins  are  present :  (1)  the 
precaval  vein  and  its  branches,  which  bring  blood  from  the  for- 
ward part  of  the  body ;  (2)  the  postcaval  vein  and  its  branches, 
which  bring  blood  from  the  hinder  part  of  the  body ;  and  (3)  the 
coronary  veins,  which  bring  blood  from  the  walls  of  the  heart 
itself. 

The  postcaval  system.  The  anterior,  thoracic  portion  of  the 
postcaval  vein  will  be  observed  later  when  the  organs  of  the 
thoracic  cavity  are  studied.  Its  abdominal  portion  arises  in 
the  hinder  part  of  the  abdominal  cavity,  and  passes  forward  near 
the  median  plane  between  the  kidneys  to  the  right  lobe  of  the 
liver,  through  which  it  passes.  It  then  pierces  the  diaphragm 
and  enters  the  thoracic  cavity. 

Press  the  liver  back  and  observe  this  large  vein  passing 
through  the  diaphragm  from  the  liver.  Press  the  liver  forward 
and  note  where  the  vein  enters  it  from  behind.  Find  the  two 
renal  veins,  which  come  to  it  from  the  kidneys.  The  postcaval 
will  be  seen  to  be  formed  in  the  hinder  part  of  the  abdomen  by 
the  union  of  two  large  veins,  the  common  iliacs,  which  bring  blood 
from  the  hind  legs. 


232  VERTEBRATE   ZOOLOGY 

As  the  vein  passes  forward  from  this  point  it  receives  the 
following  veins,  all  of  which  are  paired,  but  the  members  of  a 
pair  not  always  meeting  the  postcaval  in  the  same  transverse 
plane :  the  iliolumbalis  veins,  which  join  the  postcaval  just  in 
front  of  the  common  iliacs,  coming  from  the  lumbar  muscles ;  the 
spermatic  veins  (in  the  male),  or  the  ovarian  veins  (in  the  female), 
which  join  the  postcaval  just  behind  the  kidneys  (the  left  vein 
often  going  to  the  left  renal  vein  instead  of  to  the  postcaval) ; 
the  renal  veins,  which  bring  blood  from  the  kidneys ;  the  adreno- 
lumbalis  veins,  which  meet  the  postcaval  just  in  front  of  the 
renal  veins,  bringing  blood  from  the  abdominal  wall  and  the 
suprarenal  bodies ;  the  hepatic  veins  (variable  in  number),  which 
enter  the  postcaval  just  behind  the  diaphragm,  bringing  blood 
from  the  liver;  the  phrenic  veins,  which  meet  the  postcaval  as 
it  is  passing  through  the  diaphragm,  bringing  blood  from  that 
organ. 

Observe  the  course  of  these  veins ;  follow  the  postcaval  through 
the  liver  and  find  the  hepatic  veins. 

Study  the  common  iliac  vein  and  its  branches,  but  do  not  injure 
the  arteries  which  accompany  them.  About  an  inch  from  its 
anterior  end  it  is  formed  by  the  union  of  two  veins,  —  the 
smaller  being  the  internal  iliac  or  hypogastric,  and  the  larger  the 
external  iliac.  Note  the  small  caudal,  or  sacralis  media  vein,  which 
joins  one  of  the  common  iliacs  near  its  base.  The  internal  iliac 
vein  receives  branches  from  the  bladder,  the  genital  organs,  the 
rectum,  and  the  muscles  of  the  back  and  thigh.  The  external 
iliac  is  the  principal  vein  of  the  hind  leg.  A  short  distance 
from  its  union  with  the  internal  iliac  it  receives  the  deep  femoral 
vein  from  the  muscles  of  the  thigh.  A  branch  of  this  vein,  the 
epigastric  vein,  anastomoses  with  the  internal  mammary  vein, 
which  is  a  tributary  of  the  precaval  vein  in  the  forward  part  of 
the  body.  The  external  iliac  becomes  in  the  leg  the  femoral  vein. 
Follow  it  and  its  branches.  Trace  the  epigastric  and  note  its 
relation  to  the  internal  mammary. 

Exercise  15.  Draw  a  diagram  showing  the  postcaval  vein  and 
its  branches,  so  far  as  observed. 


THE  CAT  233 

The  arteries.  Two  groups  of  arteries  may  be  distinguished  : 
(1)  the  pulmonary  arteries,  which  carry  venous  blood  to  the 
lungs ;  and  (2)  the  aorta  and  its  branches,  which  carry  arterial 
blood  to  the  tissues. 

The  aorta  is  the  great  artery  which  lies  in  the  middorsal  line 
of  the  body  cavity  and  sends  branches  to  all  the  various  organs 
of  the  body.  It  is  divided  into  two  parts,  the  thoracic  aorta  and 
the  abdominal  aorta. 

The  abdominal  aorta  lies  just  beneath  the  spinal  column  in  the 
abdominal  cavity,  and  extends  from  the  diaphragm  to  the  hinder 
end  of  the  trunk.  It  has  been  seen  while  dissecting  the  post- 
caval  vein.  Observe  carefully  its  relation  to  this  vein ;  remove 
the  vein.  Study  the  following  branches  of  the  aorta. 

The  coaliac  artery  is  a  large  median  artery  which  leaves  the 
aorta  about  two  inches  behind  the  diaphragm.  It  soon  divides 
into  three  main  branches  :  the  hepatic  artery,  which  carries  arterial 
blood  to  the  liver  and  also  sends  branches  to  the  duodenum, 
the  stomach,  and  the  pancreas ;  the  gastrica  sinistra  artery,  which 
goes  to  the  stomach;  and  the  splenic  artery,  which  goes  to  the 
spleen  and  the  pancreas. 

The  superior  mesenteric  or  anterior  mesenteric  artery  is  also  a  large 
median  artery  which  leaves  the  aorta  a  short  distance  behind 
the  coeliac  and  takes  blood  to  both  small  and  large  intestines 
and  to  the  pancreas.  Numerous  branches  go  from  it  to  these 
organs,  which  lie  in  the  mesentery  alongside  the  branches  of  the 
superior  mesenteric  vein.  Near  the  base  of  this  artery  are  two 
ganglia  and  a  network  of  nerves,  parts  of  the  solar  plexus. 

The  adrenolumbar  arteries  are  paired  vessels  which  pass  to  the 
muscles  of  the  back  ;  they  also  usually  give  off  the  phrenic  arteries, 
which  pass  forward  to  the  diaphragm. 

The  renal  arteries  are  a  pair  of  vessels  which  supply  the  kidneys 
and  suprarenal  bodies  with  blood. 

The  spermatic  arteries  (in  the  male),  or  the  ovarian  arteries  (in  the 
female),  leave  the  aorta  behind  the  kidneys  and  go  to  the  genital 
organs.  In  the  male  each  forms  part  of  the  spermatic  cord. 

The  inferior  mesenteric  or  posterior  mesenteric  artery  is  a  small 
median  vessel  which  supplies  the  large  intestine. 


234  VEBTEBRATE  ZOOLOGY 

The  iliolumbar  arteries  are  paired  vessels  which  leave  the  aorta 
a  short  distance  back  of  the  inferior  mesenteric  and  go  to  the 
muscles  of  the  back. 

The  lumbar  arteries  are  small  paired  vessels  which  pass  from 
the  dorsal  surface  of  the  aorta  to  the  muscles  of  the  back.  Seven 
pairs  are  usually  present  and  they  are  found  from  the  diaphragm 
to  the  external  iliacs. 

The  external  iliac  arteries  are  large  paired  vessels  which,  with 
their  branches,  supply  the  hind  legs.  Each  external  iliac  gives 
off,  just  before  it  leaves  the  abdominal  cavity,  the  deep  femoral 
artery,  which  goes  to  the  muscles  of  the  thigh.  A  short  distance 
from  its  beginning  this  artery  sends  out  three  branches,  one  of 
which,  the  epigastric  artery,  passes  forward  and  anastomoses  with 
the  internal  mammary  artery,  —  a  branch  of  the  subclavian  artery 
in  the  forward  part  of  the  body.  The  continuation  of  the  ex- 
ternal iliac  is  called  the  femoral  artery,  which,  with  its  branches, 
supplies  the  greater  part  of  the  leg.  Follow  these  branches. 

The  internal  iliac  or  hypogastric  arteries  are  paired  vessels  which 
leave  the  aorta  a  short  distance  behind  the  external  iliacs ;  each 
sends  branches  to  the  bladder,  rectum,  urogenital  organs,  and 
muscles. 

The  caudal  or  sacralis  media  artery  is  the  small  continuation  of 
the  aorta  which  supplies  the  tail. 

Exercise  16.  Draw  a  diagram  showing  the  abdominal  aorta  and 
its  branches,  so  far  as  observed. 

The  thoracic  cavity.  Cut  away  the  ventral  and  lateral  walls 
of  the  thorax  and  thoroughly  expose  its  cavity,  but  do  not 
remove  the  diaphragm.  The  heart  will  be  seen  in  its  pericardium. 
Immediately  in  front  of  the  pericardium  is  the  thymus  gland,  an 
elongated  pinkish  organ  of  uncertain  function.  It  varies  much 
in  size  in  different  animals ;  in  young  animals  it  may  project 
over  the  pericardium,  while  in  old  animals  it  is  much  smaller 
and  may  be  almost  entirely  wanting.  On  each  side  of  the  heart 
will  be  seen  the  pleural  sac  with  the  lung. 

Examine  the  diaphragm  carefully.  Note  its  position  in  the 
body  cavity.  Its  general  form  is  cup-shaped,  the  opening  of  the 


THE  CAT  235 

cup  looking  toward  the  abdominal  cavity.  It  will  be  seen  to 
consist  of  a  thin  plate  of  muscle  surrounding  a  transparent  cen- 
tral tendon,  the  semilunar  tendon.  The  muscular  portion  is  made 
up  of  two  parts,  —  the  dorsal  part,  and  the  ventral  and  lateral 
part.  The  former,  which  is  called  the  vertebral  portion,  extends 
from  the  semilunar  tendon  back  to  the  vertebral  column,  the 
general  direction  of  the  fibers  being  longitudinal.  The  latter, 
the  sternocostal  portion,  forms  the  larger  part  of  the  diaphragm; 
its  fibers  radiate  from  the  semilunar  tendon  to  the  lateral  and 
ventral  sides  of  the  thorax.  The  postcaval  vein  passes  through 
the  semilunar  tendon;  the  oesophagus  and  aorta  through  the 
vertebral  portion. 

Remove  the  diaphragm.  Make  a  hole  in  the  pericardium  and 
blow  into  it  with  the  blowpipe  to  determine  its  extent.  Remove 
the  pericardium  and  the  thymus  gland,  but  without  cutting  any 
of  the  blood  vessels.  Study  the  heart  and  the  thoracic  blood 
vessels. 

The  heart  is  a  large,  conical  body  and  lies  nearly  in  the  middle 
of  the  thorax ;  it  is  composed  of  two  ventricles  and  two  auricles. 
The  posterior  and  much  larger  portion  is  formed  by  the  ven- 
tricles. The  walls  of  the  right  ventricle  are  thin  and  flabby; 
those  of  the  left  ventricle  are  thick  and  firm  and  include 
the  apex  of  the  heart.  The  auricles  lie  at  the  forward  end  of 
the  heart  and  appear  as  a  pair  of  thin-walled  sacs.  The  greater 
part  of  each  auricle  is  dorsal  in  position,  with  an  extension  onto 
the  ventral  side  called  the  right  and  the  left  auricular  appendix 
respectively. 

The  two  auricles  may  be  distinguished  from  each  other  by 
their  difference  in  color,  the  right  auricle  being  much  darker 
than  the  left  because  of  the  dark-colored  venous  blood  it  con- 
tains. The  septum  separating  the  two  ventricles  is  indicated  on 
the  ventral  surface  by  the  position  of  the  coronary  artery,  which 
emerges  from  beneath  the  left  auricle  and  runs  to  the  right  of 
the  apex  on  the  outer  surface  of  the  heart. 

Study  the  great  blood  vessels  of  the  thorax  and  their  relation 
to  the  heart.  Thoroughly  dissect  the  fat  and  other  loose  tissues 
from  them,  being  very  careful  not  to  cut  them.  Note  the  numerous 


236  VERTEBRATE  ZOOLOGY 

nerves  which  accompany  and  surround  many  of  the  vessels  at 
the  forward  end  of  the  heart ;  these  are  branches  of  the  sympa- 
thetic and  vagus  nerves. 

Extending  forward  from  the  anterior  end  of  the  heart  are 
three  large  vessels.  The  most  conspicuous  is  the  great  precaval 
vein,  which  is  dark  red  in  color  and  lies  at  the  right  of  the 
median  plane.  The  other  two  will  be  seen  emerging  from 
between  the  right  and  left  auricles ;  they  are  the  pulmonary 
artery  and  the  aorta.  The  former  springs  from  the  right  ven- 
tricle, on  the  ventral  side  of  the  heart,  and  is  seen  passing 
diagonally  forward  to  the  animal's  left ;  it  divides  almost  imme- 
diately into  the  right  and  left  pulmonary  arteries,  which  carry 
venous  blood  to  the  right  and  left  lungs.  These  arteries  may 
be  brought  into  view  by  turning  the  heart  forward. 

The  aorta,  which  carries  arterial  blood  to  the  entire  body, 
issues  from  the  left  ventricle  just  dorsal  to  the  pulmonary 
artery.  It  almost  immediately  makes  a  sharp  turn  to  the 
animal's  left,  and  passes  to  the  middorsal  line  of  the  thoracic 
cavity,  where  it  runs  posteriorly  just  beneath  the  vertebral 
column  to  the  hinder  end  of  the  body  cavity ;  it  is  thus  composed 
of  two  divisions,  —  the  thoracic  aorta  and  the  abdominal  aorta. 

Study  the  thoracic  aorta  and  its  branches,  but  do  not  follow 
them  out  of  the  thoracic  cavity. 

The  two  small  coronary  arteries  leave  the  aorta  at  its  base  and 
supply  the  walls  of  the  heart  with  blood.  If  the  left  auricle  be 
turned  forward,  the  base  of  these  arteries  will  be  seen;  later, 
when  the  heart  is  dissected,  they  may  be  traced  to  the  aorta. 

The  innominate  artery  is  the  first  large  vessel  which  passes  for- 
ward from  the  arch  of  the  aorta,  and  lies  parallel  with  the  pre- 
caval vein ;  note  the  nerves  which  lie  along  its  left  side.  It 
gives  off  the  small  mediastinal  artery  and  then  divides  into  three 
branches,  —  the  right  and  the  left  carotid  arteries,  which  carry  blood 
to  the  head,  and  the  right  subclavian  artery,  which  goes  to  the  right 
fore  leg. 

Immediately  to  the  left  of  the  innominate  artery  is  the  left 
subclavian  artery.  It  passes  forward  parallel  with  the  innominate 
and  goes  to  the  left  fore  leg. 


\A 


THE  CAT  237 

Joining  the  aortic  arch  with  the  pulmonary  artery  is  the 
short  ligamentum  Botalli.  It  is  the  rudiment  of  an  artery  called 
the  ductus  Botalli,  which  in  the  embryo  joins  these  vessels  and 
turns  the  blood  of  the  right  ventricle  into  the  aorta  instead  of 
permitting  it  to  go  to  the  lungs.  In  young  cats  this  ligament 
is  large ;  in  old  cats  it  is  small  or  wanting. 

Turn  the  left  lung  over  to  the  right  and  observe  the  aorta 
as  it  passes  posteriorly  in  the  middorsal  line  of  the  thoracic 
cavity.  Ten  pairs  of  small  intercostal  arteries  will  be  seen  arising 
from  its  dorsal  side  and  passing  to  the  muscles  of  the  back. 
Two  small  bronchial  arteries  also  branch  off  either  from  the  aorta 
near  the  fourth  intercostals,  or  from  these  intercostals  them- 
selves, and  extend  along  the  bronchi  to  the  lungs.  A  number 
of  small  arteries  also  go  to  the  oesophagus. 

Exercise  17.  Draw   the   ventral   aspect   of    the   heart   and   the 
thoracic  blood  vessels  just  mentioned. 

Turn  the  apex  of  the  heart  to  the  left  side  and  pin  it  .there. 
Study  the  dorsal  surface  of  the  heart.  Find  the  right  and  the 
left  auricles.  Note  the  precaval  vein  entering  the  right  auricle  ; 
a  short  distance  from  the  base  of  this  vein  it  is  joined  by  the 
azygos  vein.  This  is  a  median  vein  which  arises  in  the  abdom- 
inal cavity  and  extends  along  the  middorsal  line  of  the  thorax 
to  the  precaval.  It  receives  the  paired  intercostal  veins,  and  is 
homologous  to  the  right  posterior  cardinal  vein  of  fishes. 

Entering  the  posterior  margin  of  the  right  auricle  will  be 
seen  the  large  postcaval  vein,  which  brings  the  blood  of  the  entire 
hinder  part  of  the  body ;  it  receives  no  branches  in  the  thorax. 
Beneath  the  base  of  the  postcaval  the  largest  of  the  coronary  veins, 
which  bring  blood  from  the  wall  of  the  heart,  enters  the  right 
auricle. 

Entering  the  left  auricle  are  the  pulmonary  veins,  which  bring 
arterial  blood  from  the  lungs.  They  are  arranged  in  three 
groups,  each  of  which  contains  two  or  three  veins.  The  right- 
hand  and  the  left-hand  groups  bring  blood  from  the  anterior 
and  middle  lobes  of  the  right  and  the  left  lungs  respectively, 


238  VEKTEBEATE  ZOOLOGY 

the   posterior  group   from  the  posterior  lobes  of  both  lungs. 
Follow  them  to  the  lungs  and  note  their  distribution. 

Exercise  18.  Draw  the  dorsal  aspect  of  the  heart  with  the  veins 
just  mentioned. 

The  precaval  system.  The  precaval  vein  and  its  posterior 
branch,  the  azygos  vein,  have  already  been  observed.  A  short 
distance  in  front  of  the  azygos  the  precaval  receives  the  internal 
mammary  veins ;  they  unite  and  form  a  single  vessel,  which  joins 
the  precaval  opposite  the  third  rib.  Each  internal  mammary 
may  be  followed  posteriorly  to  the  abdominal  cavity,  where  it 
anastomoses  with  the  epigastric  vein. 

-The  precaval  vein  is  not  long ;  it  is  formed  by  the  union  of 
the  two  large  innominate  veins.  These  are  also  short ;  they  are 
diagonal  in  position  and  each  is  formed  by  the  union  of  the 
external  jugular  vein,  which  comes  from  the  head,  and  the  sub- 
clavian,  from  the  shoulder  and  fore  leg.  The  innominate  usually 
receives  a  single  tributary,  which  is  formed  by  the  union  of  the 
vertebral  and  costocervical  veins,  although  these  are  subject  to 
considerable  variation.  The  vertebral  veins  return  blood  from  the 
cranial  cavity ;  they  lie,  one  on  each  side,  in  the  vertebrarterial 
canals  of  the  anterior  six  cervical  vertebrse  ;  the  costocervical  veins 
bring  blood  from  the  muscles  of  the  back  and  neck. 

The  subclavian  forms  the  proximal  portion  of  the  system  of 
veins  which  brings  blood  from  the  shoulder  and  the  fore  leg; 
lateral  to  the  wall  of  the  thorax  it  is  called  the  axillary  vein, 
which  receives  several  small  tributaries  and  is  formed  by  the 
union  of  two  veins,  the  subscapular  and  the  brachial.  The  former 
of  these  brings  blood  from  the  shoulder.  The  brachial  vein 
comes  from  the  leg.  Follow  these  veins  and  their  branches  on 
the  right  side  of  the  body,  being  careful  not  to  injure  the  arteries 
which  accompany  them. 

The  external  jugular  vein  lies  just  beneath  the  skin  on  the  side 
of  the  neck.  It  receives,  near  its  base,  the  internal  jugular  vein. 
Follow  this  large  vein  and  the  external  jugular  forward  on  the 
right  side  of  the  body.  The  internal  jugular  lies  at  the  side  of 
the  trachea  alongside  a  prominent  nerve,  the  vagus,  and  the 


THE  CAT  239 

carotid  artery  ;  it  arises  at  the  base  of  the  skull  and  returns 
blood  from  the  brain.  The  external  jugular  is  formed  at  the 
base  of  the  head  by  the  union  of  the  anterior  facial  vein,  which 
arises  beneath  the  eye  and  brings  blood  from  the  lower  portion 
of  the  face,  and  the  posterior  facial  vein,  which  collects  blood  from 
the  upper  and  hinder  portions  of  the  head.  Near  their  origin 
the  right  and  left  external  jugulars  are  connected  by  the  trans- 
verse vein,  which  passes  across  the  throat. 

Near  the  base  of  the  internal  jugular  the  external  jugular 
receives  the  thoracic  duct.  This  is  the  main  lymph  canal  of  the 
body  ;  it  comes  from  the  region  of  the  large  mesenteric  lymph 
glands  and  lies  along  the  left  side  of  the  aorta  and  the  oasophagus. 
It  will  be  seen  with  difficulty,  if  at  all. 

Note  the  thyroid  gland.  It  is  a  large  double  gland  near  the 
forward  end  of  the  neck;  it  consists  of  two  elongated  lobes, 
which  lie  on  either  side  of  the  trachea,  and  a  ventrally  situated 
connecting  lobe. 

Exercise  19.  Draw  a  diagram  showing  the  veins  of  the  precaval 
system,  so  far  as  observed. 

The  anterior  arteries.  Study  the  right  subclavian  artery  and  its 
main  branches.  The  first  of  these  to  leave  the  subclavian  is 
the  vertebral  artery.  This  artery  branches  off  from  the  dorsal  side 
of  the  subclavian  at  the  first  rib,  passes  forward,  and  enters  the 
vertebrarterial  canal,  in  which  it  goes  to  the  head.  It  enters 
the  foramen  magnum  and,  joining  the  left  vertebral  artery, 
forms  the  median  basilar  artery  of  the  brain. 

The  internal  mammary  artery  leaves  the  ventral  side  of  the 
subclavian  near  the  vertebral  artery  and  passes  back  along  the 
inner  surface  of  the  sternum  to  the  abdominal  cavity,  where  it 
finally  anastomoses  with  the  epigastric  artery. 

The  costocervical  artery  arises  from  the  subclavian  just  back  of  the 
vertebral  artery ;  it  divides  at  once  into  two  branches  which  supply 
the  intercostal  muscles  and  the  muscles  of  the  back  and  sides. 

The  thyrocervical  axis  arises  opposite  the  internal  mammary 
artery  and  passes  forward  to  the  muscles  of  the  shoulder  and 
neck  and  to  the  thyroid  gland. 


240  VERTEBRATE   ZOOLOGY 

The  continuation  of  the  subclavian  is  called  the  axillary  artery. 
It  lies  immediately  behind  the  brachial  plexus,  which  is  a  net- 
work of  large  nerves  in  the  axillary  region.  It  gives  off  two 
small  arteries  and  then  divides  into  the  subscapular  and  the 
brachial.  The  former  passes  toward  the  shoulder,  where  it  gives 
off  branches  which  supply  the  muscles  of  the  shoulder.  The 
brachial  artery  goes  to  the  arm,  which  it  supplies  with  blood. 
Follow  these  arteries  and  their  branches. 

Exercise  20.  Draw  a  diagram  showing  the  distribution  of  the 
subclavian  artery  and  its  branches,  so  far  as  observed. 

Study  the  right  carotid  artery  and  its  branches,  which  passes 
forward  alongside  the  trachea  to  the  head.  Just  in  front  of 
the  thyroid  gland  it  gives  off  the  thyroid  artery.  The  muscularis 
artery  branches  off  very  near  the  thyroid  and  goes  to  the  muscles 
of  the  neck.  At  the  base  of  the  neck  the  large  lingual  artery  goes 
to  the  under  side  of  the  face  and  to  the  tongue,  and  the  external 
maxillary  to  the  side  of  the  face.  At  the  base  of  the  ear  the 
posterior  auricular  artery  passes  to  the  muscles  of  the  ear  and 
the  head,  and  the  temporal  artery  also  to  the  muscles  of  the  head. 
The  carotid  artery  then  ends  in  a  network  of  small  arteries 
near  the  base  of  the  jaw,  called  the  carotid  plexus. 

Exercise  21.  Draw  a  diagram  showing  the  distribution   of  the 
carotid  artery  and  its  branches  so  far  as  observed. 

The  internal  structure  of  the  heart.  Remove  the  heart  from 
the  body,  cutting  its  veins  and  arteries  a  short  distance  from 
it,  and  dissect  it  under  water.  Pin  the  heart  with  the  ventral 
side  uppermost  and  thoroughly  dissect  away  the  loose  tissues 
from  the  stumps  of  the  aorta  and  the  pulmonary  artery.  Iden- 
tify the  ligamentum  Botalli,  which  joins  the  two,  and  cut  it. 
Note  at  the  base  of  the  aorta  the  beginning  of  the  coro- 
nary arteries.  Pin  the  heart  with  the  dorsal  side  uppermost ; 
identify  and  clean  the  stumps  of  the  precaval,  postcaval,  and 
pulmonary  veins. 

Slit  open  the  dorsal  wall  of  the  right  auricle  and  its  append- 
age, but  without  injuring  the  caval  veins,  and  wash  out  the 


THE  CAT  241 

blood  inside.  Note  the  network  of  muscles  on  the  inner  sur- 
face, also  the  openings  of  the  caval  veins  into  the  auricle. 
Just  posterior  to  the  postcaval  opening  is  that  of  the  small 
coronary  vein,  in  front  of  which  is  a  valve.  Observe  the  auric- 
ular septum,  which  separates  the  two  auricles,  and  the  oval 
depression,  the  fossa  ovalis.  In  the  embryo  an  opening  called 
the  foramen  ovale  is  present  at  this  place,  through  which  the 
fetal  blood  passes  directly  from  the  right  to  the  left  auricle, 
instead  of  going  first  through  the  right  ventricle  and  to  the 
lungs.  Note  the  large  auriculo-ventricular  aperture  into  the  right 
ventricle. 

Open  the  right  ventricle  by  slitting  the  pulmonary  artery 
longitudinally  and  continuing  the  incision  to  the  hinder  end 
of  the  ventricle.  Note  the  thinness  of  the  walls  of  the  ven- 
tricle and  the  muscular  ridges  on  the  inner  surface.  Guarding 
the  auriculo-ventricular  aperture  is  the  large  tricuspid  valve, 
which  consists  of  a  long  membranous  flap  attached  at  its  free 
end  to  the  wall  of  the  ventricle  by  long  tendinous  and  mus- 
cular cords,  the  chordae  tendineae.  The  opening  of  the  ventricle 
into  the  pulmonary  artery  is  guarded  by  the  three  pouched 
semilunar  valves,  which  permit  the  flow  of  blood  only  in  one 
direction.  Look  for  them  with  the  aid  of  the  blowpipe. 

Slit  open  the  dorsal  wall  of  the  left  auricle,  but  without 
cutting  the  pulmonary  veins.  Note  the  three  openings  of  the 
pulmonary  veins,  and  the  large  auriculo-ventricular  aperture. 

Open  the  left  ventricle  by  slitting  the  aorta  and  continuing 
the  incision  through  the  ventricle  to  the  apex  of  the  heart, 
and  study  the  interior.  Note  the  thickness  of  its  walls.  The 
auriculo-ventricular  aperture  is  guarded  by  the  bicuspid  or  mitral 
valve,  which  consists  of  two  distinct  flaps  joined  with  the  ven- 
tricular wall  by  chordae  tendinese.  The  opening  into  the  aorta 
is  guarded  by  three  semilunar  valves,  one  of  which  is  dorsal  and 
the  other  two  lateral.  Note  the  two  prominent  muscular  ridges 
—  the  columnae  carneae  —  in  the  wall  of  the  ventricle. 

Exercise  22.    Draw  a  diagrammatic  view  showing  the  four  cavi- 
ties of  the  heart  and  their  apertures  and  valves. 


242  VERTEBRATE  ZOOLOGY 

Cut  off  the  apex  of  the  heart  by  a  transverse  incision  a  quar- 
ter of  an  inch  from  the  end,  showing  the  two  ventricles  and 
the  relative  thickness  of  their  walls. 

Exercise  23.  Draw  the  cross  section. 

Exercise  24.  Draw  a  diagram  showing  the  entire  vascular  system. 

The  mouth  and  the  pharynx ;  the  salivary  glands.  Skin  the 
head.  Five  pairs  of  these  glands  are  present,  all  of  which  open 
into  the  mouth. 

The  parotid  glands  are  the  largest.  Each  is  situated  just  beneath 
the  skin  and  immediately  below  the  ear ;  its  duct  passes  through 
to  the  inner  surface  of  the  cheek,  where  it  opens  into  the  mouth 
opposite  the  last  premolar  tooth. 

The  submaxillary  glands  are  situated  just  below  and  behind 
the  parotids.  The  duct  of  each  runs  forward  and  opens  at  the 
end  of  a  papilla  in  the  forward  part  of  the  floor  of  the  mouth, 
near  the  median  line. 

The  sublingual  glands  are  situated  in  front  of  the  submaxillaries 
and  in  contact  with  them.  The  duct  of  each  passes  forward 
and  opens  into  the  mouth  at  the  apex  of  the  same  papilla. 

The  molar  gland  extends  from  just  beneath  the  angle  of  the 
mouth  posteriorly;  it  is  very  small  and  opens  into  the  mouth 
by  a  number  of  ducts. 

The  infraorbital  gland  lies  on  the  ventral  wall  of  the  orbit.  It 
will  be  seen  when  the  orbit  is  dissected.  Its  duct  opens  into 
the  mouth  just  back  of  the  upper  molar. 

Exercise  25.  Draw  an  outline  of  the  head  and  show  the  position 
of  the  salivary  glands. 

Cut  away  the  lips  and  expose  the  teeth.  Shut  the  jaws 
and  observe  the  relation  of  the  teeth  of  the  lower  jaw  to  those 
of  the  upper.  The  dental  formula  of  the  cat  is  the  following : 
incisors  |,  canines  l,  premolars  f ,  molars  1.  The  milk  teeth  of 
the  young  cat  lack  the  molars. 

Exercise  26.  Draw  a  front  and  also  a  side  view  of  the  closed 
mouth,  with  outlines  of  the  teeth. 


THE  CAT  243 

Cut  through  the  muscles  on  each  side  of  the  head  from  the 
angle  of  the  mouth  to  the  end  of  the  jaw.  Disarticulate  the 
lower  jaw,  first  cutting  it  with  bone  forceps,  if  necessary,  and 
turn  it  down,  exposing  the  cavities  of  the  mouth  and  pharynx. 
The  two  cavities  form  a  single  space  which  extends  from  the 
lips  to  the  beginning  of  the  oesophagus.  The  mouth  is  much 
the  larger  of  the  two  spaces,  and  extends  from  the  lips  to  the 
free  edge  of  the  soft  palate  ;  the  pharynx  lies  between  this  point 
and  the  oesophagus,  and  is  the  space  in  which  the  path  of  the 
respiratory  air  from  the  nostrils  to  the  lungs  crosses  that  of  the 
food  from  the  mouth  to  the  stomach. 

The  mouth  cavity  itself  is  made  up  of  two  regions,  —  the  vesti- 
bule, which  is  that  part  between  the  lips  and  cheeks  and  the  jaws 
and  teeth ;  and  the  mouth  proper,  or  that  part  between  the  teeth 
and  the  soft  palate.  A  median  fold  called  the  frenulum  unites 
the  upper  lip  with  the  jaw.  The  lower  lip  and  the  lower  jaw 
are  also  united  by  frenula,  not  only  in  the  median  plane  but 
also  on  each  side  just  back  of  the  canine  teeth. 

The  roof  of  the  mouth  is  formed  by  the  hard  and  the  soft 
palate.  The  hard  palate,  which  forms  the  anterior  portion,  is 
characterized  by  a  number  of  curved,  transverse  ridges,  between 
which  are  rows  of  papillae.  Between  the  anterior  ridge  and  the 
incisor  teeth  is  a  large  median  papilla,  on  each  side  of  which  is 
the  opening  of  the  duct  leading  to  the  organ  of  Jacobson,  a  small 
sensory  organ  of  uncertain  function  which  lies  on  the  floor  of 
the  nasal  cavity. 

The  soft  palate  is  the  soft  flap  which  forms  the  hinder  portion 
of  the  roof  of  the  mouth ;  it  will  be  seen  to  be  much  narrower 
than  the  hard  palate.  The  narrow  space  forming  the  hinder 
part  of  the  mouth  cavity,  which  is  bounded  dorsally  by  the  soft 
palate  and  by  the  root  of  the  tongue  ventrally,  is  called  the 
isthmus  faucium.  Diverging  from  either  side  of  the  soft  palate 
to  the  side  of  the  tongue  and  the  ventral  wall  of  the  pharynx 
are  two  folds  called  the  anterior  and  the  posterior  pillars  of  the 
fauces.  From  each  of  the  lateral  sides  of  the  isthmus  between 
these  pillars  a  prominent  lobed  gland  called  the  tonsil  projects 
into  the  cavity. 


244  VERTEBRATE  ZOOLOGY 

The  floor  of  the  mouth  is  formed  principally  by  the  tongue, 
which  is  a  muscular  organ  projecting  from  it.  The  free  end 
of  the  tongue  is  joined  with  the  floor  of  the  mouth  by  means 
of  a  median  fold  called  the  frenulum  linguae. 

The  upper  surface  of  the  tongue  is  provided  with  three  kinds 
of  papillae,  —  the  filiform,  fungiform,  and  circumvallate.  The 
filiform  papillae  cover  the  upper  surface,  those  on  the  middle 
and  forward  portions  having  sharp,  horny  tips  which  form  the 
rasping  surface  peculiar  to  carnivorous  mammals ;  the  fungiform 
papillae  are  enlarged  at  their  free  ends,  and  are  the  prominent 
projections  in  the  middle  and  at  the  sides  of  the  tongue  near 
its  root,  those  at  the  sides  being  very  large;  the  circumvallate 
papillae  are  prominent  projections,  each  surrounded  by  a  circular 
groove  and  a  ridge,  which  are  present  in  two  rows  of  two  or 
three  papillse  each,  at  the  posterior  part  of  the  tongue  between 
the  lateral  fungiform  papillse. 

The  pharynx  lies  just  back  of  the  soft  palate.  Two  passages 
open  into  it  at  its  anterior  and  two  at  its  posterior  end.  The 
two  anterior  passages  are  the  isthmus  faucium,  the  hinder  end 
of  the  mouth,  and  the  nasopharynx.  This  latter  space  is  a  part 
of  the  respiratory  passage.  It  lies  immediately  above  the  soft 
palate  and  the  hinder  part  of  the  hard  palate,  and  communicates 
posteriorly  with  the  pharynx  and  anteriorly  with  the  nasal  cav- 
ities. Probe  it  and  determine  its  extent. 

The  two  posterior  openings  of  the  pharynx  are  the  oesophagus 
and  the  glottis.  The  latter  is  the  opening  into  the  larynx  and 
is  ventral  to  the  oesophagus ;  it  is  guarded  by  the  epiglottis,  a 
triangular  cartilage  which  acts  as  a  valve  and  closes  the  glottis 
when  food  is  passing  through  the  pharynx. 

Exercise  27.  Draw  a  diagrammatic   sketch  showing  the  cavity 
of  the  mouth  and  pharynx. 

The  respiratory  system.  This  system  consists  of  the  nasal 
cavities,  the  nasopharynx,  the  pharynx,  the  trachea  with  the 
larynx,  the  bronchi,  and  the  lungs. 

The  nasal  cavities  are  two  in  number  and  lie  side  by  side  in 
the  anterior  portion  of  the  head,  separated  by  a  median  partition, 


THE  CAT  245 

the  nasal  septum.  They  communicate  with  the  outside  by  the 
nostrils  or  anterior  nares,  and  with  the  nasopharynx  by  the  posterior 
nares.  Cut  away  the  soft  palate  and  the  hinder  part  of  the  hard 
palate  and  expose  the  nasopharynx  and  the  posterior  nares. 
Note  a  pair  of  slits  in  the  lateral  walls  near  the  middle  of  the 
nasopharynx ;  these  are  the  openings  of  the  Eustachian  tubes, 
which  join  the  middle  ear  with  the  pharynx. 

The  nasal  cavities  are  rendered  very  irregular  in  outline  and 
are  almost  entirely  filled  by  projections  from  their  walls.  These 
projections  are  called  the  turbinals  and  serve  to  increase  the 
sensory  surface ;  they  will  be  studied  with  the  skeletal  system. 

Make  a  transverse  section  of  the  anterior  end  of  the  nose, 
using  a  large  scalpel.  The  cartilaginous  nasal  septum  will  be 
seen  between  the  two  nostrils.  From  its  dorsal  edge  on  each 
side  a  thin  plate  passes  laterally,  then  ventrally,  and  finally 
dorsally,  forming  the  sides  of  the  cavity. 

Exercise  28.  Draw  the  transverse  section. 

Observe  the  trachea  arid  the  larynx,  and  the  organs  lying  near 
them.  Just  dorsal  to  the  trachea  is  the  oesophagus,  a  long  mus- 
cular tube  which  extends  from  the  pharynx  to  the  stomach. 
On  each  side  of  the  trachea  is  the  carotid  artery  and  the  internal 
jugular  vein,  and  also  a  nerve  cord  which  is  composed  of  the 
vagus  and  sympathetic  nerves  closely  bound  together;  these 
nerves  must  not  be  cut.  Near  the  anterior  end  of  the  trachea 
is  the  thyroid  gland. 

Dissect  from  the  body  the  tongue  with  its  long  supporting 
hyoid  bones,  the  larynx  and  trachea,  and  the  lungs,  and  bring 
them  into  a  pan  of  water.  Do  not  cut  the  nerve  cord  just  men- 
tioned. Note  the  relation  of  the  hyoid  apparatus  to  the  larynx. 
Carefully  dissect  away  the  tongue  and  expose  the  hyoid.  It  will 
be  seen  to  consist  of  a  transverse  median  bone,  the  basihyal,  and 
two  pairs  of  horns  or  cornua.  The  anterior  cornua  are  the  longer 
and  consist  of  four  bony  segments  on  a  side ;  the  posterior 
cornua  are  composed  of  a  single  bone  on  each  side. 

Study  the  larynx,  first  removing  the  muscles  from  its  sides. 
The  glottis,  the  opening  into  the  larynx  from  the  pharynx,  is  a 


246  VERTEBRATE  ZOOLOGY 

triangular  slit  in  the  floor  of  the  pharynx,  in  front  of  which  is 
the  epiglottis.  The  larynx,  which  controls  the  passage  of  air  into 
and  from  the  lungs  and  produces  the  voice,  is  made  up  of  plates 
of  cartilage  connected  by  ligaments  and  muscles.  There  are 
three  large,  unpaired  cartilages,  the  thyroid,  cricoid,  and  epiglottis ; 
and  a  pair  of  small  cartilages,  the  arytenoids.  The  thyroid  carti- 
lage is  the  large  plate  on  the  ventral  and  lateral  sides,  which 
forms  the  anterior  ring  of  the  larynx.  The  cricoid  is  just  behind 
the  thyroid;  it  forms  a  complete  ring,  which  is  wide  dorsally 
and  narrow  ventrally.  The  arytenoid  cartilages  are  two  small 
triangular  bodies  which  articulate  with  the  anterior  edge  of  the 
dorsal  side  of  the  cricoid  cartilage,  in  the  median  line. 

On  either  side  of  the  glottis,  at  the  base  of  the  epiglottis,  is 
a  pair  of  fleshy  ridges,  the  false  vocal  cords ;  the  vibration  of  these 
cords  is  said  to  produce  purring.  Just  behind  these  are  the 
true  vocal  cords.  They  are  a  pair  of  ridges  on  the  inner  surface 
of  the  larynx,  which  converge  from  the  arytenoid  cartilages  dor- 
sally to  the  inner  surface  of  the  thyroid  cartilage  ventrally. 

Exercise  29.  Draw  a  semidiagrammatic  sketch  of  the  anterior 
end  of  the  larynx,  showing  the  false  and  the  true  vocal 
cords,  together  with  the  hyoid  bones. 

Study  the  trachea,  the  bronchi,  —  which  are  formed  by  the 
branching  of  the  hinder  end  of  the  trachea,  —  and  the  lungs. 
The  cartilaginous  rings  of  the  trachea  are  incomplete  on  the 
dorsal  side  where  it  lies  against  the  oesophagus.  The  structure 
of  the  bronchi  is  similar  to  that  of  the  trachea.  The  lungs  are 
large-lobed  organs,  the  right  lung  being  divided  into  four  lobes 
and  the  left  lung  into  two :  the  anterior  lobe  of  the  left  lung  is 
subdivided  into  two  lobes.  A  branch  of  the  bronchus  penetrates 
into  each  lobe.  Dissect  a  branch  of  the  bronchus  and  follow  it 
as  far  as  possible  into  the  lung. 

Exercise  30.  Make  a  drawing  of  the  ventral  surface  of  the  lungs, 
the  bronchi,  and  the  trachea. 

The  nervous  system.  This  system  is  composed  of  (1)  the 
central  nervous  system,  or  the  brain  and  the  spinal  cord ;  (2)  the 


THE  CAT  247 

peripheral  nervous  system,  which  is  composed  (a)  of  the  paired 
cranial  and  spinal  nerves  and  (b)  the  sympathetic  nervous  sys- 
tem ;  and  (3)  the  special  sense  organs. 

We  shall  first  study  the  spinal  nerves  and  the  sympathetic 
system. 

Thirty-eight  pairs  of  spinal  nerves  are  present,  of  which  eight 
are  cervical,  thirteen  thoracic,  seven  lumbar,  three  sacral,  and 
usually  seven  or  eight  caudal.  With  the  exception  of  the  first 
two  pairs,  all  the  spinal  nerves  pass  from  the  neural  canal  through 
openings  between  the  vertebrae,  called  intervertebral  foramina.  The 
first  pair  passes  through  a  pair  of  foramina  in  the  dorsal  arch  of 
the  atlas,  and  the  second  pair  between  the  arches  of  the  atlas 
and  axis.  Each  nerve  arises  from  the  spinal  cord  by  two 
roots  which  join  immediately  outside  the  intervertebral  fora- 
men. Of  these  roots  the  dorsal  one  bears  a  ganglion  and  is 
sensory  in  function,  while  the  ventral  root  is  motor.  Immedi- 
ately after  its  formation  by  the  meeting  of  these  roots,  the  spinal 
nerve  divides  into  two  branches,  —  a  smaller  dorsal  and  a  larger 
ventral  ramus. 

At  each  end  of  the  trunk  the  spinal  nerves  unite  and  form  a 
complicated  network  called  a  nerve  plexus.  That  at  the  ante- 
rior end  is  the  brachial  plexus.  It  lies  in  the  axillary  region  near 
the  shoulder,  and  is  formed  of  the  ventral  rami  of  the  fifth, 
sixth,  seventh,  and  eighth  cervical,  and  the  first  thoracic  nerves; 
the  nerves  which  arise  from  it  go  to  the  arm  and  shoulder. 

Identify  the  roots  of  these  five  nerves ;  that  of  the  fifth  cer- 
vical is  the  smallest,  the  others  are  large  and  conspicuous. 
Carefully  free  the  plexus  of  the  surrounding  tissue  and  follow 
the  main  nerves  which  spring  from  it.  The  arrangement  of  the 
network  is  quite  variable.  The  following  are  the  principal 
nerves  which  leave  the  plexus. 

The  radial  nerve  is  the  largest.  It  arises  from  the  seventh  and 
eighth  cervical  and  the  first  thoracic  nerves,  and  is  distributed  to 
the  muscles  and  skin  of  the  fore  leg. 

The  median  nerve,  which  is  formed  by  the  .union  of  branches 
from  the  seventh  and  eighth  cervical  and  the  first  thoracic 
nerves,  and  the  ulnar  nerve,  which  springs  from  the  eighth 


248  VEKTEBRATE  ZOOLOGY 

cervical  and  the  first  thoracic,  are  large  nerves  which  accompany 
the  brachial  artery  into  the  leg. 

The  musculo-cutaneous  nerve  is  formed  by  the  union  of  branches 
of  the  sixth  and  seventh  thoracic  nerves.  It  supplies  the  biceps 
and  other  muscles  of  the  upper  arm  and  the  skin  of  the  forearm. 

The  axillary  nerve  is  formed  by  branches  of  the  sixth  and 
seventh  cervical  nerves  and  passes  to  the  muscles  and  skin  of 
the  shoulder. 

The  subscapular  nerves  are  three  in  number;  they  arise  from 
the  sixth,  seventh,  and  eighth  cervical  nerves  and  go  to  the 
subscapular  muscle  on  the  inner  surface  of  the  scapula. 

The  suprascapular  nerve  arises  from  the  sixth  cervical  nerve  and 
goes  to  the  muscles  of  the  outer  surface  of  the  scapula  and  to 
the  integument  of  the  upper  arm. 

The  phrenic  nerve  is  formed  by  the  union  of  a  branch  from  the 
fifth  and  one  from  the  sixth  cervical  nerve ;  it  passes  directly 
back,  at  first  along  the  subclavian  artery,  to  the  diaphragm. 

Exercise  31.  Draw  a  diagram  of  the  brachial  plexus  and  the 
nerves  which  issue  from  it,  so  far  as  observed. 

The  thoracic  spinal  nerves,  with  the  exception  of  the  first,  do  not 
enter  a  plexus,  but  go  directly  to  the  muscles  of  the  back  and 
side.  Their  dorsal  rami  are  small ;  their  ventral  rami  are  large 
and  are  called  the  intercostal  nerves ;  each  lies  alongside  the  hinder 
border  of  a  rib,  together  with  the  intercostal  artery.  Find  one 
of  these  nerves  and  trace  it  to  the  backbone,  where  the  dorsal 
ramus  will  also  be  seen. 

The  first  three  lumbar  spinal  nerves  do  not  enter  a  plexus. 
Their  ventral  rami  divide  a  short  distance  from  their  medial 
ends  into  an  anterior  and  a  posterior  division.  Look  for  the  first 
pair  of  lumbar  nerves  a  short  distance  behind  the  last  rib  and 
beneath  the  muscle  which  forms  the  inner  layer  of  the  abdomi- 
nal wall.  The  two  divisions  of  the  ventral  ramus  will  here  be 
found.  Trace  them  medially  and  find  the  dorsal  ramus.  Find 
the  second  and  third  lumbar  nerves. 

The  fourth,  fifth,  sixth,  and  seventh  lumbar  nerves  and  the 
three  pairs  of  sacral  nerves  form  the  lumbosacral  plexus ;  the  nerves 


THE  CAT  249 

issuing  from  it  supply  the  hind  legs  and  the  hinder  part  of  the 
trunk.  This  plexus  is  partly  hidden  by  muscles  and  may  be  best 
studied  by  finding  the  nerves  which  issue  from  it  and  following 
them  back  to  the  plexus. 

The  largest  of  these  nerves  are  the  great  sciatic,  the  obturator, 
and  the  femoral  nerves.  The  first  of  these  is  the  largest  nerve  in 
the  body ;  it  is  a  great  cord  which  will  be  seen  passing  straight 
back  through  the  pelvis.  It  is  formed  principally  by  the  union 
of  the  sixth  and  seventh  lumbar  and  the  first  and  second  sacral 
nerves.  Trace  it  forward,  thoroughly  removing  the  muscle  and 
fat  which  obscure  it.  Note  its  two  largest  roots,  which  are  the 
seventh  lumbar  and  the  first  sacral  nerves.  Follow  the  great 
sciatic  into  the  leg. 

Just  in  front  of  the  great  sciatic  is  the  obturator  nerve.  Trace 
it  forward;  it  will  be  found  to  be  formed  by  the  union  of  the 
sixth  and  seventh  spinal  nerves. 

The  femoral  is  a  large  nerve  which  is  formed  by  the  union  of 
branches  of  the  fifth  and  sixth  lumbar  nerves ;  it  is  covered  up 
by  a  muscle,  which  must  be  removed.  As  it  emerges  from  the 
abdominal  cavity  it  divides  into  three  nerves  which  supply 
the  muscles  of  the  thigh.  One  of  these  —  the  saphenous  — is  the 
long  nerve  which  accompanies  the  femoral  vein  and  artery. 

The  genitofemoral  nerve  arises  principally  from  the  fourth  lum- 
bar nerve  and  passes  to  the  anterior  surface  of  the  thigh.  It 
divides  into  two  main  branches ;  one  of  these  passes  through 
the  longitudinal  muscle  which  lies  alongside  the  spinal  column 
in  the  abdominal  cavity,  and  appears  on  its  ventral  surface ;  the 
other  passes  posteriorly  along  the  medial  surface  of  this  muscle. 

The  lateral  cutaneous  nerve  arises  principally  from  the  fifth  lum- 
bar nerve  and  passes  through  the  abdominal  wall  to  the  posterior 
side  of  the  thigh. 

Study  the  three  sacral  nerves.  The  first  sacral  is  the  hinder- 
most  of  the  two  large  nerves  which  form  the  main  roots  of  the 
great  sciatic  nerve. 

Exercise  32.  Draw  a  diagram  of  the  lumbosacral  plexus  and  the 
nerves  which  issue  from  it,  so  far  as  observed. 


250  VEETEBEATE   ZOOLOGY 

The  dorsal  rami  of  the  caudal  spinal  nerves  supply  the  dorsal 
side  of  the  tail ;  the  ventral  rami  are  connected  with  one  another 
and  with  the  last  sacral  nerve  by  a  longitudinal  nerve. 

The  sympathetic  system  consists  of  two  rows  of  small  ganglia 
which  lie  on  either  side  of  the  spinal  column  against  the  dorsal 
wall  of  the  body  cavity  and  in  the  neck,  those  of  each  row  being 
connected  with  one  another  by  a  longitudinal  nerve,  and  with 
the  spinal  nerves  by  short  branch  nerves ;  they  are  also  connected 
with  various  organs  of  the  thoracic  and  abdominal  cavities  by 
numerous  nerves  which  in  certain  places  form  plexuses. 

The  sympathetic  system  falls  into  three  divisions,  the  cervical, 
thoracic,  and  abdominal.  The  thoracic  and  abdominal  divisions 
which  lie  in  the  cavities  of  the  same  names  are  easily  studied. 
The  two  longitudinal  nerves  will  here  be  seen  lying  against 
the  dorsal  body  wall  on  either  side  of  the  spinal  column. 
In  the  abdominal  cavity  they  lie  nearer  together  than  in  the 
thoracic,  gradually  becoming  smaller  toward  the  posterior  end 
of  the  abdominal  cavity,  where  they  finally  come  to  an  end. 
In  both  these  cavities  a  pair  of  sympathetic  ganglia  is  present 
opposite  each  vertebra,  and  a  short  connecting  nerve  joins  each 
ganglion  with  a  spinal  nerve. 

Look  for  the  longitudinal  sympathetic  nerves,  first  in  the 
abdominal  cavity,  where  they  lie  against  the  vertebrae.  Note 
the  sympathetic  ganglia  here  and  follow  the  connecting  nerves 
which  join  them  with  the  corresponding  spinal  nerves.  Follow 
then  the  longitudinal  nerves  into  the  thoracic  region. 

In  the  cervical  region  the  longitudinal  sympathetic  nerve  is 
so  closely  joined  with  the  vagus  that  they  appear  like  a  single 
strand;  this  lies  along  the  trachea  together  with  the  carotid 
artery  and  the  internal  jugular  vein.  A  short  distance  in  front 
of  the  first  rib  they  separate  from  each  other,  and  the  sympa- 
thetic, which  is  the  smaller  and  more  dorsal  of  the  two,  passes 
into  the  thorax. 

Three  large  ganglia  lie  in  the  course  of  the  cervical  portion  of 
the  sympathetic  cord  on  each  side,  —  the  anterior,  middle,  and  pos- 
terior cervical  ganglia.  The  first  of  these  marks  the  anterior  end  of 
the  sympathetic  system  ;  it  is  a  large  ganglion  just  back  of  the 


THE  CAT  251 

base  of  the  skull  on  the  side  of  the  neck  and  close  to  the  ganglion 
nodulosum  of  the  vagus.  The  other  two  are  at  the  base  of  the 
neck  near  the  first  rib,  and  are  joined  together  by  two  nerves. 

Two  large  nerve  plexuses,  the  cardiac  and  the  solar,  and  sev- 
eral smaller  ones,  belong  to  the  sympathetic  system.  The  cardiac 
plexus  lies  at  the  anterior  end  of  the  heart,  around  the  base  of 
the  aorta  and  the  pulmonary  artery.  The  solar  plexus  lies  between 
the  fundus  of  the  stomach,  the  dorsal  portion  of  the  diaphragm, 
the  suprarenal  bodies,  and  the  aorta.  It  consists  of  two  ganglia 
—  the  large  coeliac  or  semilunar  ganglion  which  lies  near  the  supe- 
rior mesenteric  artery,  and  the  smaller  mesenteric  ganglion  —  and  of 
nerves  which  radiate  from  these  ganglia  in  all  directions.  These 
ganglia  are  joined  with  the  longitudinal  sympathetic  nerve  by 
several  nerves,  of  which  the  great  splanchnic  is  the  largest.  This 
nerve  separates  from  the  sympathetic  in  the  thorax,  pierces  the 
diaphragm,  and  goes  directly  to  the  cceliac  ganglion. 

Exercise  33.  Draw  a  diagram  of  the  sympathetic  system,  so  far 
as  observed. 

The  special  sense  organs ;  the  nose.  This  has  already  been 
dissected.  The  entire  surface  of  the  nasal  cavity  is  not  pro- 
vided with  an  olfactory  mucous  membrane.  Of  the  two  prin- 
cipal passages  on  each  side,  the  lower  one  is  purely  respiratory 
in  function  and  transmits  air  into  the  pharynx  ;  the  upper  pas- 
sage is  olfactory  in  function  and  in  it  the  olfactory  nerve  is 
distributed. 

The  eye.  The  eyeball,  together  with  its  muscles,  glands,  and 
other  accessory  organs,  lies  within  a  membranous  sac  called  the 
periorbita,  which  almost  completely  fills  the  bony  orbit.  Toward 
the  outside  the  eye  is  protected  by  the  upper  and  lower  eyelids 
and  the  nictitating  membrane.  The  eyelids  are  folds  of  the 
skin ;  they  have  no  eyelashes,  but  are  covered  with  hair,  like 
the  rest  of  the  body.  On  the  inner  surface  of  the  lid,  near  the 
edge,  are  the  Meibomian  glands;  they  are  oil  glands  and  appear 
as  parallel  yellow  bands. 

The  nictitating  membrane  is  situated  at  the  inner  corner 
of  the  eye,  over  which  it  moves.  Pull  it  with  forceps.  It  is 


252  VEKTEBKATE  ZOOLOGY 

stiffened  by  a  cartilage  whose  position  is  shown  by  the  ridge  it 
produces.  A  thin  transparent  membrane  called  the  conjunctiva 
covers  the  inner  surface  of  the  eyelids,  the  exposed  surface  of 
the  eye,  and  both  sides  of  the  nictitating  membrane. 

Observe  the  exposed  portion  of  the  eyeball.  The  convex, 
transparent  cornea  forms  its  outer  portion.  The  yellow  iris  will 
be  seen,  in  the  middle  of  which  is  the -pupil,  the  opening  through 
which  light  is  admitted  into  the  interior  of  the  eye;  the  iris 
contains  delicate  muscle  fibers  by  the  contraction  of  which  the 
pupil  is  made  smaller. 

Exercise  34.  Draw  a  sketch  showing  the  exposed  portion  of  the 
eye  and  the  lids. 

Carefully  cut  away  the  eyelids  and  the  bony  arch  which 
forms  the  lateral  wall  of  the  orbit.  Observe  the  lachrymal  gland; 
it  is  a  large,  flattened,  reddish  body,  which  often  has  the  appear- 
ance of  a  broad  muscle  and  lies  close  to  the  hinder  side  of  the 
eyeball  at  the  outer  angle  of  the  eye,  in  contact  with  the  bony 
arch.  The  fluid  furnished  by  the  gland  bathes  the  cornea  and 
is  then  drained  off  through  the  two  lachrymal  canals,  each  of 
which  opens  at  the  edge  of  one  of  the  lids  near  the  inner  angle 
of  the  eye.  These  two  canals  join  to  form  the  nasolachrymal  duct, 
which  passes  through  the  bony  wall  of  the  orbit  and  opens  into 
the  nose. 

The  muscles  of  the  orbit.  Ten  small  muscles  control  the 
movements  of  the  eyeball.  Eight  of  these  are  straight  muscles 
and  pass  from  the  inner  portion  of  the  orbit  near  the  entrance 
of  the  optic  nerve  to  the  sides  of  the  eyeball.  Of  these  the 
four  larger  are  called  the  rectus  muscles ;  the  four  smaller,  which 
lie  between  the  rectus  muscles,  are  the  four  heads  of  a  single 
muscle,  the  retractor.  The  other  two  muscles  are  the  inferior 
and  superior  oblique  muscles.  Besides  these  an  eleventh  muscle 
is  present  which  moves  the  upper  lid. 

The  lateral  and  posterior  portion  of  the  bony  orbit  being 
removed  and  the  lachrymal  gland  identified,  note  the  muscle 
which  is  the  most  anterior  in  position  of  those  exposed.  It 
lies  on  the  outer  side  of  the  eyeball,  parallel  to  the  margin 


THE  CAT  253 

of  the  cornea,  and  is  the  inferior  oblique.  It  is  inserted  in  the 
outer  surface  of  the  eyeball  near  the  cornea  and  passes  ven- 
trally  beneath  the  eyeball  to  its  origin  in  the  anterior  surface 
of  the  orbit. 

Inserted  in  the  eyeball  just  back  of  the  inferior  oblique  is  a 
broad  muscle  which  passes  straight  back  to  the  hinder  part  of  the 
orbit ;  this  is  the  external  rectus  muscle.  Along  its  posterior  border 
lies  the  lachrymal  gland;  remove  the  gland,  also  any  fat  that 
may  be  present,  and  sharply  define  the  sides  of  the  muscle.  On 
each  side  of  it  is  one  of  the  four  heads  of  the  retractor  muscle. 

Just  beneath  the  middle  of  the  inferior  oblique  is  the  inser- 
tion of  the  inferior  rectus  muscle,  which  passes  straight  back  along 
the  ventral  side  to  the  hinder  part  of  the  orbit. 

Dorsal  to  the  external  rectus  and  separated  from  it  by  the 
head  of  the  retractor  muscle  just  mentioned  is  the  superior  rectus 
muscle,  which  arises  in  the  hinder  portion  of  the  orbit  and  passes 
straight  forward  to  its  insertion  in  the  dorsal  surface  of  the 
eyeball.  Passing  over  the  outer  surface  of  this  muscle  and 
parallel  with  it  is  a  narrow  strand  of  muscle  which  goes  to 
the  margin  of  the  upper  eyelid ;  it  is  called  the  levator  muscle  of 
the  upper  eyelid. 

Just  forward  of  the  insertion  of  the  superior  rectus  is  that 
of  the  superior  oblique  muscle.  Its  tendon  runs  at  right  angles  to 
that  of  the  superior  rectus  toward  the  dorsal  margin  of  the 
inner  side  of  the  orbit,  where  it  passes  through  a  fibrous  loop ; 
here  its  direction  is  changed  and  it  goes  antero-ventrally  to 
the  body  of  the  muscle  which  lies  against  the  medial  side  of  the 
eyeball.  Its  origin  is  on  the  inner  wall  of  the  orbit,  just  in 
front  of  the  optic  foramen. 

Cut  the  tendon  of  the  superior  oblique,  press  the  eye  ventrally, 
and  find,  on  the  medial  side  of  the  eyeball,  the  internal  rectus  muscle, 
which  extends  from  its  insertion  near  the  dorsal  margin  of  the 
eyeball  straight  back  to  its  origin  in  the  inner  wall  of  the  orbit. 
On  each  side  of  it  is  one  of  the  heads  of  the  retractor  muscle. 

Exercise  35.    Draw   a   diagram   showing    the   eyeball   and   its 
muscles. 


254  VERTEBRATE   ZOOLOGY 

Pull  the  eyeball  forward  and  cut  the  optic  nerve  and  the 
muscles.  Remove  the  eyeball  from  the  orbit  and  cut  away  the 
muscles  and  fat  still  attached  to  it.  It  will  be  seen  to  be  a 
spherical  structure  the  anterior  surface  of  which  is  somewhat 
flattened.  Its  outer  covering  is  the  sclerotic  coat,  a  thick,  tough 
membrane  of  connective  tissue,  the  anterior  portion  of  which 
is  the  transparent  cornea.  The  boundary  between  the  cornea 
and  the  sclerotic  is  marked  by  a  prominent  white  ridge. 

With  sharp  scissors  cut  two  large  openings  in  the  side  of 
the  eyeball,  opposite  each  other,  and  study  the  interior  of  the 
eye.  Carefully  remove  the  other  eye  from  the  orbit  and  cut  it 
in  two  by  an  equatorial  incision.  Note  behind  the  pupil  the 
large,  transparent  crystalline  lens;  do  not  disturb  it.  The  layer 
just  within  the  sclerotic  is  the  choroid  coat,  the  anterior  portion 
of  which  is  the  iris.  The  choroid  coat  contains  the  blood  vessels 
of  the  eye  and  the  pigment.  Within  the  white  ridge  of  the 
sclerotic  just  mentioned  the  choroid  is  thickened  by  the  pres- 
ence of  a  large  number  of  radiating  ridges  which  form  the 
ciliary  body.  This  structure  forms  thus  a  broad  black  ridge 
around  the  inner  surface  of  the  eye.  Extending  inward  from 
this  ridge  is  a  delicate  membrane  called  the  suspensory  ligament ; 
this  is  continuous  with  the  transparent  capsule  in  which  the 
lens  is  suspended.  Delicate  muscle  fibers  are  present  in  the 
choroid  near  the  ciliary  body,  by  which  the  position  of  the  crys- 
talline lens  is  changed  when  the  focus  of  the  eye  is  adjusted. 
A  layer  of  cells,  called  the  tapetum  lucidum,  which  has  a  metallic 
sheen  and  reflects  the  light,  is  present  in  the  choroid  coat,  in 
the  region  of  the  optic  nerve ;  it  causes  the  cat's  eyes  to  shine 
in  the  dark. 

The  inner  coat  of  the  eye  is  the  retina.  It  is  a  soft,  delicate 
membrane  which  will  often  be  found  separated  from  the  cho- 
roid; it  is  the  sensitive  portion  of  the  eye,  and  is  in  direct 
connection  with  the  optic  nerve.  The  point  where  the  nerve 
pierces  the  sclerotic  and  choroid  coats  and  joins  the  retina  is 
shown  by  a  small  round  spot,  called  the  blind  spot  because  the 
sensitive  elements  of  the  retina  are  here  absent.  Anteriorly 
the  retina  gradually  becomes  thinner  and  ends  on  the  inner 


THE  CAT  255 

surface  of  the  iris.  Just  behind  the  ciliary  body  it  forms  a 
serrated  ridge  called  the  ora  serrata. 

The  crystalline  lens  is  a  large,  double-convex,  transparent  body 
situated  immediately  behind  the  iris;  its  convexity  is  greater 
on  the  anterior  than  on  the  posterior  side.  It  is  suspended  in  a 
delicate  capsule  which  is  attached  to  the  ciliary  body  by  the 
suspensory  ligament. 

The  interior  of  the  eye  is  divided  into  two  principal  chambers 
by  the  lens  and  the  iris.  The  posterior  cavity  is  rilled  with  a 
jellylike  mass  called  the  vitreous  humor,  the  anterior  cavity  with 
a  fluid  mass  called  the  aqueous  humor. 

Exercise  36.  Draw  a  diagram  showing  the  structure  of  the  eye. 
Carefully  label  all  of  the  parts. 

The  ear.  The  organ  of  hearing  is  made  up  of  three  parts,  — 
the  internal  ear  or  membranous  labyrinth,  the  essential  auditory 
organ,  which  is  situated  in  a  bony  capsule  at  the  side  of  the 
cranium ;  the  middle  ear,  or  tympanic  cavity,  in  which  are  the 
ear  ossicles  and  the  tympanic  membrane  ;  and  the  outer  ear. 

The  outer  ear  is  composed  of  the  external  ear,  which  extends 
above  the  head  and  receives  the  vibrations  of  sound,  and  the 
external  auditory  meatus,  the  canal  which  leads  to  the  tympanic 
cavity.  The  external  ear,  whose  movements  are  controlled  by 
small  muscles,  is  a  thin  plate  of  cartilage,  covered  on  both  sides 
by  integument. 

The  middle  ear.  Cut  away  the  cartilaginous  walls  of  the 
external  auditory  meatus  until  the  bony  walls  of  the  skull  are 
reached.  At  the  inner  end  of  the  meatus  is  the  tympanic  mem- 
brane, or  eardrum,  surrounded  by  a  ridge  of  bone.  Note  its 
shape  and  the  character  of  the  membrane.  The  middle  ear  lies 
in  the  tympanic  bulla,  which  is  the  spherical  projection  of  the 
skull  just  back  of  the  external  ear.  Entirely  free  this  from  the 
muscles  which  may  be  attached  to  it.  With  a  strong  scalpel 
cut  away  the  medial  wall  of  the  bulla  and  expose  its  interior. 
This  is  divided  into  a  medial  and  a  lateral  chamber  by  a  bony 
partition  extending  from  its  lateral  wall.  Of  these  two  cham- 
bers the  lateral  one  is  the  tympanic  cavity  proper  and  contains 


256  VEKTEBRATE  ZOOLOGY 

the  ear  ossicles ;  from  the  forward  end  the  Eustachian  tube  goes 
to  the  nasopharynx.  Note  the  round  hole  in  the  dorsal  wall; 
this  is  the  fenestra  rotunda. 

Carefully  cut  away  the  partition  between  the  chambers  until 
the  inner  surface  of  the  tympanic  membrane  appears,  and  study 
it  and  the  ear  bones.  There  are  three  of  these  bones,  —  the 
hammer  or  malleus,  the  anvil  or  incus,  and  the  stirrup  or  stapes. 
The  hammer  consists  of  two  parts,  —  a  slender  handle  and  a 
large,  irregularly  shaped  head.  The  handle  extends  across  the 
dorsal  portion  of  the  tympanic  membrane,  above  the  hinder 
rim  of  which  the  head  is  situated.  The  anvil  is  a  minute  bone 
with  two  projections,  which  articulates  with  the  head  of  the 
hammer  by  one  of  its  limbs  and  with  the  stirrup  by  the  other. 
The  last  named  bone,  which  has  the  form  of  a  stirrup,  fits  into 
the  fenestra  ovalis,  an  opening  into  the  inner  ear;  this  opening 
is  just  medial  to  the  ridge  surrounding  the  fenestra  rotunda. 

Exercise  37.  Draw  a  diagrammatic  sketch  of  the  inner  surface 
of  the  tympanic  membrane,  together  with  the  hammer  and 
the  fenestra  rotunda. 

Thoroughly  clean  out  the  middle  ear.  Two  minute  muscles 
are  present  in  it  which  are  inserted  in  the  hammer  and  the 
stirrup.  Observe  the  grooves  in  the  walls  of  the  cavity. 

Exercise  38.  Draw  a  view  of  the  walls  exposed  and  show  the 
two  fenestrse  and  the  Eustachian  canal. 

The  inner  ear.  The  membranous  labyrinth  is  an  irregular  sac 
entirely  inclosed  in  the  bony  capsule  called  the  bony  laby- 
rinth. It  communicates  with  the  middle  ear  by  two  openings, 

—  the  fenestra  ovalis  and  the  fenestra  rotunda,  just  mentioned, 

—  and  consists  of  three  main  portions,  —  the  vestibule,  the  cochlea, 
and  the  semicircular  canals.    The  cochlea  is  situated  in  the  prom- 
inent ridge  which  appears  just  back  of  the  fenestra  ovalis.    The 
vestibule  is  behind  the  cochlea,  which  extends  from  it  on  one  side, 
while  from  the  opposite  side  project  the  semicircular  canals. 

The  bone  within  which  the  membranous  labyrinth  lies  is  very 
hard  and  thick,  and  a  dissection  of  the  labyrinth  is  impossible 


THE  CAT  257 

without  a  special  treatment  of  the  bone.  If,  however,  this  por- 
tion of  the  skull  be  decalcified  in  a  ten  per  cent  solution  of  nitric 
acid,  the  labyrinth  can  be  studied. 

The  central  nervous  system  ;  the  brain.  Before  removing  the 
brain  from  the  cranial  cavity  cut  away  the  skin  and  the  muscles 
from  the  head  and  the  adjacent  portions  of  the  neck ;  remove 
also  the  tongue  and  the  lower  jaw.  With  bone  forceps  chip 
away  the  roof  of  the  skull.  Do  not  tear,  if  possible,  the  dura 
mater,  the  outermost  of  the  coatings  of  the  brain,  which  lies 
next  to  the  inner  surface  of  the  skull,  but  press  it  away  from 
the  skull  as  the  removal  of  the  bone  continues.  Expose  thus 
the  dorsal  and  lateral  surfaces  of  the  brain.  Take  pains  to  pre- 
serve intact  the  olfactory  lobes  which  form  the  anterior  end  of 
the  brain.  Special  care  must  also  be  taken  in  removing  the  ten- 
torium,  the  vertical  bony  partition  which  extends  from  the  roof 
of  the  skull  between  the  cerebrum  and  the  cerebellum.  Remove 
now  the  dura  mater  from  the  dorsal  and  lateral  sides  of  the 
brain. 

The  brain  and  spinal  cord  are  enveloped  in  three  membranes, 
—  the  dura  mater,  the  thick  outer  membrane,  the  pia  mater,  the 
thin  inner  membrane,  and  the  delicate  arachnoid,  between  the 
other  two. 

Study  the  dorsal  surface  of  the  brain.  It  is  made  up  of  five 
divisions,  —  the  cerebrum,  the  anterior  and  largest  division ; 
the  thalamencephalon ;  the  midbrain ;  the  cerebellum ;  and  the 
medulla  oblongata,  which  is  continuous  with  the  spinal  cord. 
Of  these  five  divisions  the  first  and  fourth  occupy  almost  the 
entire  dorsal  surface.  The  cerebrum  is  divided  by  a  median  longi- 
tudinal cleft,  called  the  sagittal  fissure,  into  the  two  hemispheres, 
at  the  anterior  ends  of  which  are  the  olfactory  lobes. 

The  area  of  the  surface  of  the  cerebrum  will  be  seen  to  be 
very  much  increased  by  the  presence  of  folds,  the  gyri,  which 
are  separated  from  one  another  by  deep  fissures  called  sulci. 
These  gyri  are  characteristic  of  mammals,  all  of  which,  except 
the  lowest,  possess  them.  The  surface  of  each  hemisphere  is 
divided  into  four  principal  gyri  whose  general  position  is  longi- 
tudinal, and  whose  margins  are  not  in  all  places  distinct. 


258  VERTEBRATE  ZOOLOGY 

Lateral  to  the  sagittal  fissure  is  the  marginal  gyrus,  which  is 
sometimes  double  posteriorly.  Lateral  to  this  gyrus  and  sepa- 
rated from  it  by  the  lateral  sulcus  is  the  suprasylvian  gyrus.  Lateral 
to  this  gyrus  and  separated  from  it  by  the  suprasylvian  sulcus  is 
the  ectosylvian  gyrus,  the  form  of  which  is  that  of  an  inverted  U. 
Between  the  limbs  of  this  gyrus  is  the  Sylvian  gyrus,  which  forms 
an  inverted  V,  the  two  limbs  of  which  are  separated  by  the 
short  Sylvian  fissure.  Between  the  Sylvian  and  the  ectosylvian 
gyri  is  the  ectosylvian  sulcus,  which  is  not  complete  but  is  inter- 
rupted dorsally.  On  the  ventrolateral  surface,  beneath  the  Syl- 
vian fissure,  is  the  pyriform  lobe,  which  is  continuous  with  the 
olfactory  lobe.  Just  back  of  and  above  the  olfactory  lobe  at  the 
anterior  end  of  the  hemisphere  is  the  orbital  gyrus,  and  behind 
that  the  sigmoid  gyrus,  with  the  presylvian  and  cruciate  sulci  between 
them,  the  former  being  ventral  to  the  latter.  Along  the  hinder 
margin  of  the  hemisphere  is  the  posterior  gyrus. 

Behind  the  cerebrum  is  the  cerebellum.  Its  surface  is  also 
marked  by  the  presence  of  gyri  and  sulci,  which  have,  however, 
a  different  appearance  from  those  of  the  cerebrum.  Three  gen- 
eral regions  are  distinguishable,  —  the  median  vermis  and  the 
lateral  hemispheres. 

Back  of  the  cerebrum  and  partly  covered  by  it  is  the  fifth 
division  of  the  brain,  the  medulla  oblongata.  Posteriorly  it  de- 
creases in  width  and  is  continuous  with  the  spinal  cord. 

Exercise  39.  Make  a  semidiagrammatic  drawing  of  the  dorsal 
aspect  of  the  brain. 

Chip  away  the  side  of  the  skull  and  expose  the  entire  lateral 
aspect  of  the  brain  and  the  roots  of  the  cranial  nerves.  Of 
these  nerves  there  are  twelve  pairs.  The  first  pair  —  the  olfac- 
tory nerves  —  pass,  in  the  form  of  many  small  fibers,  from  the 
olfactory  lobes  to  the  nose.  Tilt  the  brain  to  one  side  and 
observe  the  large  optic  nerves,  the  second  pair  of  cranial  nerves, 
also  the  optic  chiasma,  from  which  they  spring. 

Back  of  the  hemispheres  is  the  broad  pons  with  its  transverse 
fibers;  it  is  the  ventral  portion  of  the  fourth  division  of  the 
brain,  of  which  the  cerebellum  is  the  dorsal  portion.  Just  in 


THE   CAT  259 

front  of  it  and  springing  from  near  the  median  line  may  be  seen, 
by  tilting  the  brain  to  one  side,  the  small  oculomotor  nerves,  the 
third  pair  of  cranial  nerves,  which  pass  forward  on  each  side 
and  supply  the  following  muscles  of  the  eyeball:  the  superior 
rectus,  medial  rectus,  retractor,  inferior  rectus,  and  inferior 
oblique.  From  the  lateral  side  of  the  brain  just  in  front  of  the 
pons  on  each  side  springs  the  pathetic  or  trochlear  nerve,  the  fourth 
cranial  nerve ;  it  is  a  delicate  strand  which  passes  forward  to 
the  superior  oblique  muscle  of  the  eyeball.  It  will  be  seen  when 
the  ventral  surface  of  the  brain  is  studied. 

The  large  trigeininal  nerve  —  the  fifth  cranial  —  springs  from 
the  posterior  border  of  the  pons  by  two  roots,  a  small  motor 
and  a  large  sensory  root.  The  large  root  passes  straight  forward, 
and  soon  enlarges  and  forms  the  Gasserian  ganglion,  from  which 
three  nerves  spring,  —  the  ophthalmic,  the  maxillary,  and  the  man- 
dibular ;  the  small  root  joins  the  last-named  nerve.  The  ophthal- 
mic nerve  passes  into  the  orbit,  where  it  gives  off  branches  which 
go  to  the  eyeball,  the  upper  eyelid,  and  the  nose  and  snout.  The 
maxillary  nerve  emerges  from  the  cranium  back  of  the  orbit  and 
gives  off  branches  which  go  to  the  lower  eyelid,  the  upper  lip 
and  jaw,  the  palate,  and  the  face.  The  mandibular  nerve  leaves 
the  cranial  cavity  back  of  the  orbit  and  gives  off  branches  which 
supply  the  external  ear,  the  muscles  of  the  jaw,  the  lower  jaw, 
the  lips,  and  the  tongue. 

Just  back  of  the  pons  will  be  seen  in  the  lateral  aspect  of 
the  brain  a  swelling  called  the  trapezium,  which  is  the  anterior 
end  of  the  medulla.  Springing  from  the  medulla  medial  to  the 
trapezium  is  the  sixth  pair  of  cranial  nerves,  the  abducens,  which 
pass  to  the  lateral  rectus  muscle  of  the  eyeball;  these  nerves 
will  be  seen  when  the  ventral  surface  of  the  brain  is  studied. 

Arising  from  the  lateral  surface  of  the  trapezium  are  the 
facial  and  the  auditory,  the  seventh  and  eighth  cranial  nerves. 
The  facial  is  the  smaller  of  the  two;  it  springs  from  near  the 
base  of  the  trigeminal  nerve  and  passes  to  the  face  immediately 
below  the  external  ear,  where  it  gives  off  branches  which  sup- 
ply the  muscles  of  the  face.  The  auditory  is  a  large  nerve  just 
behind  the  facial,  which  passes  directly  to  the  inner  ear. 


260  VEETEBEATE  ZOOLOGY 

In  exposing  the  remaining  cranial  nerves  take  great  care  not  to 
break  them,  as  they  arise  by  fine  roots  which  are  easily  injured. 

The  ninth  and  tenth  cranial  nerves  —  the  glossopharyngeal  and 
the  vagus  —  arise  from  the  side  of  the  medulla  back  of  the  audi- 
tory nerve,  each  by  a  number  of  small  roots,  and  leave  the  cranial 
cavity  together  immediately  behind  the  tympanic  bulla.  The 
glossopharyngeal  passes  backward  and  sends  branches  to  the 
pharynx  and  tongue ;  it  is  the  sensory  nerve  of  the  tongue. 

The  vagus  passes  along  the  neck  on  each  side,  bound  together 
with  the  sympathetic  nerve,  giving  off  branches  to  the  pharynx 
and  larynx.  Two  ganglia  —  the  ganglion  jugulare  and  the  ganglion 
nodulosum  —  are  present  in  it  near  the  point  where  it  leaves  the 
cranial  cavity,  the  former  being  in  front  of  the  latter. 

At  the  hinder  end  of  the  neck  the  vagus  and  the  sympathetic 
separate  from  each  other  and  enter  the  thorax.  The  former,  which 
is  the  larger  of  the  two,  soon  gives  off  the  inferior  laryngeal  nerve, 
which  runs  forward  alongside  the  trachea  to  the  larynx ;  it  then 
passes  to  the  anterior  end  of  the  lung,  where  it  breaks  into  numer- 
ous branches.  These  form  networks  about  the  base  of  the  lungs 
and  the  heart,  which  are  called  the  pulmonary  plexus  and  the  cardiac 
plexus.  Two  of  these  branches  pass  back,  on  each  side,  to  the  stom- 
ach, where  they  form  the  anterior  and  the  posterior  gastric  plexuses. 

The  spinal  accessory  —  the  eleventh  cranial  nerve  —  is  formed 
by  the  union  of  numerous  roots  which  arise  along  the  lateral 
surface  of  the  medulla  and  spinal  cord.  It  passes  with  the  spinal 
cord  into  the  cranium  through  the  foramen  magnum,  and  then 
out  again  together  with  the  vagus  and  glossopharyngeal  nerves ; 
it  supplies  the  muscles  of  the  neck. 

The  hypoglossal  —  the  twelfth  cranial  nerve  —  arises  from  the 
ventral  surface  of  the  medulla  by  a  number  of  roots.  It  passes 
from  the  cranial  cavity  to  the  muscles  of  the  neck  and  tongue ; 
it  is  the  motor  nerve  of  the  tongue. 

Exercise  40.  Draw  a  semidiagrammatic  view  of  the  lateral  aspect 
of  the  brain,  showing  the  cranial  nerves  so  far  as  observed. 

Study  the  ventral  surface  of  the  brain.  Separate  the  brain  from 
its  attachments  and  remove  it  from  the  body.  In  taking  it  out 


THE  CAT  261 

note  the  hypophysis,  a  median  projection  of  the  ventral  surface 
back  of  the  optic  nerves ;  it  is  lodged  in  a  depression  of  the  floor 
of  the  cranial  cavity  and  may  be  torn  off  in  removing  the  brain. 

At  the  anterior  end  of  the  hemispheres  are  the  olfactory  lobes, 
and  back  of  them,  the  olfactory  tracts.  Still  farther  back  is  a 
pair  of  triangular  swellings  called  the  substantia  perforata  anterior, 
because  they  are  pierced  by  many  small  blood  vessels. 

These  structures  belong  to  the  cerebrum,  the  anterior  divi- 
sion of  the  brain.  Back  of  them  are  those  which  belong  to  the 
thalamencephalon,  the  second  division.  These  are,  first,  the  optic 
nerves,  and  the  optic  chiasma  from  which  they  spring ;  the  chiasma 
is  formed  by  the  meeting  of  the  optic  tracts,  one  of  which  comes 
from  each  side.  Back  of  the  chiasma  is  the  tuber  cinereum,  a 
rather  extensive  median  swelling ;  from  it  projects  the  infundib- 
ulum,  which  bears  at  its  end  the  hypophysis  or  pituitary  body. 
Just  back  of  the  tuber  cinereum  are  two  white  projections,  the 
mammary  bodies.  On  each  side  of  these  structures  is  the  large 
pyriform  lobe  of  the  cerebrum. 

Back  of  the  mammary  bodies  are  the  pedunculi  cerebri,  which 
belong  to  the  third  division  of  the  brain,  the  midbrain.  They 
are  a  pair  of  semicylindrical  bodies  which  proceed  from  beneath 
the  pyriform  lobes  backward,  converging  toward  the  median  line. 
Between  the  pedunculi  is  an  area  called  the  substantia  perforata 
posterior.  The  oculomotor  nerves  spring  from  this  region. 

The  pons,  a  broad  belt  of  transverse  fibers  divided  in  two  by 
a  median  groove,  follows  posteriorly;  it  belongs  to  the  fourth 
division  of  the  brain.  At  the  anterior  border  of  its  lateral  ends 
the  delicate  trochlear  nerves  arise. 

Back  of  the  pons  are  the  structures  which  belong  to  the 
medulla,  the  fifth  division  of  the  brain.  They  are  the  two  tra- 
pezia, one  on  each  side,  and  in  the  median  area  between  them  a 
pair  of  elongated  pyramidal  tracts,  which  extend  far  back  of  them. 
At  the  sides  of  these  tracts  and  behind  the  trapezia  on  each 
side  is  the  area  elliptica,  lateral  to  which  is  the  area  ovalis. 

Exercise  41.  Draw  an  outline  sketch  of  the  ventral  aspect  of 
the  brain,  showing  accurately  these  structures. 


262  VERTEBRATE  ZOOLOGY 

Study  the  internal  structure  of  the  brain.  The  brain,  like 
the  spinal  cord,  is  a  hollow  structure.  Unlike  the  spinal  cord, 
however,  in  which  the  cavity  is  a  simple  tubular  canal,  the 
cavities  of  the  brain  form  a  series  of  complicated  spaces  which 
extend  throughout  its  five  divisions  and  their  outgrowths. 
The  brain  has  thus  dorsal,  ventral,  and  lateral  walls,  which 
surround  these  spaces.  These  walls  vary  much  in  thickness  in 
different  places,  the  actual  form  of  the  brain  being  largely  due 
to  these  variations. 

We  shall  study  first  a  longitudinal  median  section  of  the 
brain.  Cut  the  brain  with  a  large,  sharp  scalpel,  or  a  razor, 
into  two  equal  halves  by  a  sagittal  incision.  Observe  the  gyri 
and  sulci  on  the  medial  surface  of  the  hemisphere.  Observe 
the  conspicuous,  broad  band  of  white  fibers  which  joins  the 
two  hemispheres;  this  is  the  corpus  callosum.  Its  posterior  end 
is  called  the  splenium  and  is  not  so  thick  as  the  anterior 
portion.  The  point  where  it  turns  down  anteriorly  is  called 
the  genu;  the  anterior  end,  which  turns  slightly  posteriorly,  is 
called  the  rostrum.  Extending  ventrally  from  the  ventral  sur- 
face of  the  corpus  callosum  is  a  white  arched  band  of  longi- 
tudinal fibers  which  is  called  the  fornix.  In  the  angle  between 
the  anterior  half  of  the  corpus  callosum  and  the  fornix  is  the 
septum  pellucidum.  It  is  a  vertical  partition  between  the  two 
anterior  ventricles  of  the  brain,  one  of  which  is  in  each  hemi- 
sphere. At  the  ventral  end  of  the  fornix  is  a  small  band  of 
white  fibers  called  the  anterior  commissure,  which  extends  between 
the  hemispheres.  Extending  straight  ventrally  from  this  com- 
missure is  a  thin  plate,  the  lamina  terminalis,  which  appears  in 
the  section  as  a  thin  line;  it  is  the  forward  boundary  of  the 
third  ventricle  of  the  brain,  and  bears  at  its  ventral  end  the 
optic  chiasma. 

The  third  ventricle,  which  is  in  the  second  division  of  the 
brain,  is  a  very  narrow,  slitlike  space  which  lies  behind  the 
lamina  terminalis ;  if  the  section  be  not  exactly  median,  it  may 
not  come  into  view.  Its  lateral  walls  are  formed  on  each  side 
by  the  optic  thalamus.  Ventrally,  the  ventricle  is  continued  into 
the  tuber  cinereum  and  the  infundibulum. 


THE  CAT  263 

In  the  dorsal  portion  of  the  third  ventricle  and  lying  just 
behind  the  fornix  will  be  seen  the  circular  cross  section  of  a 
large  body,  the  middle  commissure ;  it  joins  the  two  thalami. 

The  dorsal  wall  of  the  third  ventricle  is  a  thin  membrane 
which  is  joined  with  the  vascular  pia  mater  and  forms  with  it 
the  anterior  choroid  plexus;  it  is  situated  in  the  bend  of  the 
fornix  and  may  be  torn  away  when  the  section  is  made.  In 
the  hinder  part  of  the  dorsal  wall,  and  just  beneath  the  sple- 
nium,  is  a  small  conical  thickening,  the  pineal  body  or  epiphysis. 

Back  of  these  structures  is  the  midbrain.  The  extension  of 
the  third  ventricle  backward  into  the  midbrain  is  called  the 
aqueductus  Sylvii ;  it  will  be  seen  to  be  a  straight,  longitudinal 
canal.  In  its  dorsal  wall  are  four  thickenings  called  the  corpora 
quadrigemina,  which  extend  back  to  the  cerebellum  ;  its  ventral 
wall  is  much  thicker  than  the  dorsal,  and  forms  the  pedunculi 
cerebri,  which  extend  back  to  the  pons. 

The  fourth  and  fifth  divisions  of  the  brain  are  behind  the 
midbrain.  Their  cavity  is  the  fourth  ventricle,  which  extends 
back  from  the  aqueductus  Sylvii  and  is  continuous  posteriorly 
with  the  central  canal  of  the  spinal  cord.  This  ventricle  is 
narrow  at  its  two  ends  and  wide  in  the  middle.  The  dorsal 
wall,  which  is  just  beneath  the  cerebellum,  will  be  seen  to  be 
very  thin,  and  is  often  torn  away  by  the  knife  in  making  the 
section.  The  hinder  portion  of  it  is  joined  with  the  vascular 
pia  mater  and  forms  the  posterior  choroid  plexus. 

The  cerebellum  is  an  outgrowth  of  the  dorsal  wall  of  the 
fourth  division  of  the  brain.  The  peculiar  branching  of  its 
numerous  folds,  especially  of  the  white  matter  as  it  appears 
in  a  longitudinal  section,  has  received  the  name  of  the  arbor 
vitae.  Note  the  great  thickness  of  the  pons  which  forms  the 
ventral  wall  of  this  division  of  the  brain. 

Exercise  42.  Draw  the  median  surface  of  the  divided  brain  and 
carefully  label  all  of  the  parts  which  appear. 

The  lateral  ventricles.  The  two  hemispheres  contain  the  first 
and  second,  or  lateral,  ventricles  and  are  bound  together,  as  we 
have  seen,  by  the  corpus  callosum  and  the  fornix.  Introduce 


264  VERTEBRATE  ZOOLOGY 

the  blade  of  a  small  scalpel  between  the  upper  surface  of  the 
corpus  callosum  and  the  hemisphere  of  the  left  half  of  the  brain, 
and  remove  the  hemisphere,  being  careful  not  to  cut  into  the 
ventricle,  the  roof  of  which  is  formed  by  the  corpus  callosum. 
Now  cut  through  the  corpus  callosum  into  the  ventricle  and 
carefully  chip  away  the  entire  roof  of  the  latter,  but  do  not 
remove  the  f ornix.  The  cavity  is  thus  fully  exposed ;  its  ante- 
rior end  is  called  the  anterior  horn,  the  posterior  portion  the  inferior 
or  posterior  horn.  The  former  passes  ventrally  and  ends  near 
the  medial  plane  in  the  anterior  portion  of  the  hemisphere ;  the 
latter  is  a  long,  narrow  passage,  semicircular  in  form,  which 
lies  in  the  posterior  lobe  of  the  hemisphere  and  parallel  to  its 
outer  surface. 

The  floor  of  the  anterior  horn  projects  into  the  cavity  and 
is  called  the  corpus  striatum.  The  floor  of  the  posterior  horn  like- 
wise projects  prominently  into  the  cavity  and  is  called  the  hip- 
pocampus. Along  the  entire  anterior  border  of  the  hippocampus 
is  a  band  called  the  fimbria,  which  is  covered  by  a  vascular 
membrane. 

The  fornix,  as  we  have  already  seen,  is  a  narrow,  median  band 
of  longitudinal  fibers  which  lies  between  the  hemispheres  just 
below  the  corpus  callosum.  It  consists  of  several  parts,  which 
cannot  be  observed  if  the  section  be  not  exactly  median.  Its 
forward  end  is  split,  forming  the  anterior  pillars  of  the  fornix, 
which  are  medial  to  the  corpus  striatum.  Just  behind  the 
pillars,  and  between  them  and  the  middle  commissure,  is  the 
foramen  of  Monro,  a  small  opening  which  joins  the  two  ventricles 
of  the  hemispheres  with  the  third  ventricle.  The  posterior  por- 
tion of  the  fornix  is  also  split,  forming  the  posterior  pillars, 
which  lie  medial  to  the  hippocampi  of  the  hemispheres.  The 
fornix,  the  hippocampus,  and  the  fimbria,  it  will  be  seen,  lie  in 
the  ventral  wall  of  the  hemisphere  and  immediately  in  front 
of  and  dorsal  to  the  third  ventricle. 

Exercise  43.  Draw  a  sketch  showing  these  structures. 

Carefully  remove  the  hippocampus  and  the  fimbria.  Beneath 
them  are  two  oblique  ridges,  —  the  paired  optic  thalami,  —  which 


THE  CAT  265 

form  the  sides  of  the  thalamencephalon,  and  between  which  is 
the  third  ventricle.  Each  thalamus  extends  laterally  and  ven- 
trally  to  the  ventral  side  of  the  brain,  where  it  becomes  the 
optic  tract;  the  two  optic  tracts  form  the  optic  chiasma  from 
which  the  optic  nerves  proceed. 

Back  of  the  optic  thalami  are  the  corpora  quadrigemina,  two 
pairs  of  elevations  which  belong  to  the  midbrain.  The  anterior 
are  somewhat  smaller  than  the  posterior. 

Remove  the  cerebellum.  The  roof  of  the  fourth  ventricle  will 
now  be  seen,  the  presence  of  which  is  marked  by  a  large  tri- 
angular depression.  The  prominent  ridge  on  each  side  of  the 
ventricle  is  the  area  ovalis. 

Exercise  44.  Draw  a  sketch  showing  these  structures. 

The  spinal  cord.  Remove  the  skin  and  muscles  from  the  ver- 
tebrae of  the  neck  and  trunk.  With  bone  forceps  remove  the 
roof  of  the  neural  arches  of  all  the  vertebrae  and  expose  the 
spinal  cord.  Note  the  spinal  nerves  issuing  from  the  inverte- 
bral  foramina,  and  their  dorsal  and  ventral  roots.  Observe  also 
the  ganglion  in  the  dorsal  root,  and  the  two  rami  of  the  nerve. 
Note  the  enlargement  of  the  cord  in  the  cervical  and  the  lum- 
bar region.  Posteriorly  the  cord  diminishes  in  size  until  it 
becomes  a  small  strand  called  the  filum  terminale,  which  goes 
into  the  tail.  In  the  sacral  and  caudal  regions  the  spinal  nerves 
are  small  and  pass  almost  directly  backward.  They  lie  thus 
close  together  and  form,  with  the  filum  terminale,  a  bunch  of 
fibers  called  the  cauda  equina.  On  both  the  dorsal  and  ventral 
sides  of  the  spinal  cord  a  median  longitudinal  fissure  is  present. 

Exercise  45.  Draw  an  outline  of  the  dorsal  surface  of  the  cord. 

Make  a  cross  section  of  the  cord  and  note  the  inner  gray  and 
the  outer  white  matter,  the  small  central  canal,  and  the  dorsal 
and  ventral  fissures. 

Exercise  46.  Draw  the  cross  section. 

The  muscular  system.  Kill  a  cat  as  directed  at  the  beginning 
of  this  dissection  and  skin  it.  The  cutaneous  muscles  will  be 


266  VERTEBRATE  ZOOLOGY 

removed  with  the  skin.  These  are  two  in  number,  the  great 
cutaneous  and  the  platysma.  The  former  is  a  very  broad,  thin, 
transparent  muscle,  which  extends  beneath  the  skin  over  almost 
the  entire  side  of  the  body.  The  latter  covers  the  sides  and 
back  of  the  neck  and  the  sides  of  the  head. 

Study  first  the  superficial  muscles  of  the  side  of  the  body. 
Remove  the  fat  which  may  overlay  any  of  these  muscles.  Note 
the  broad  white  membrane  which  covers  the  back  in  the  abdom- 
inal region :  this  is  the  lumbodorsal  fascia.  Note  also  the  narrow 
white  membrane  in  the  midventral  area :  this  is  the  linea  alba. 

On  the  side  of  the  trunk  between  the  fore  and  hind  legs  two 
large  muscles  occupy  almost  the  whole  space,  the  external  oblique 
and  the  latissimus  dorsi.  The  former  is  a  thin  plate  which  covers 
the  lateral  and  ventral  portions  of  the  abdomen.  It  arises  from 
the  last  nftie  or  ten  ribs  and  the  lumbodorsal  fascia  and  extends 
ventro-posteriorly  to  the  midventral  portion  of  the  abdomen.  The 
latter  is  a  broad  muscle  which  arises  from  the  neural  processes 
of  the  posterior  nine  thoracic  and  the  anterior  six  lumbar  ver- 
tebrae, and  passes  over  the  dorsal  portion  of  the  anterior  end  of 
the  external  oblique  to  the  forearm  and  shoulder,  where  it  is 
inserted  in  the  medial  surface  of  the  humerus.  It  draws  the 
arm  back. 

Immediately  anterior  to  this  muscle  on  the  dorsal  side  of  the 
trunk  are  the  trapezius  muscles.  The  posterior  trapezius,  or 
spinotrapezius,  arises  from  the  neural  processes  of  the  thoracic 
vertebras  and  passes  to  the  spine  of  the  scapula.  The  middle 
trapezius,  or  acromiotrapezius,  lies  in  front  of  the  last-named  muscle 
and  directly  above  the  scapula.  It  arises  along  the  middorsal 
line  of  the  neck  and  shoulder  and  passes  to  the  spine  of  the 
scapula.  The  anterior  trapezius,  or  clavotrapezius,  arises  from  the 
posterior  surface  of  the  skull  and  the  middorsal  line  of  the  neck 
and  extends  downward  along  the  sides  of  the  neck  to  the 
clavicle,  where  it  is  continuous  with  the  clavobrachial,  a  muscle 
which  extends  ventrally  to  the  ulna. 

Ventral  to  the  middle  trapezius  is  the  spinodeltoid  muscle,  which 
extends  from  the  spine  of  the  scapula  to  the  anterior  side  of  the 
humerus.  Between  the  last-named  two  muscles  and  the  anterior 


THE  CAT  267 

trapezius  are  the  acromiodeltoid  and  the  levator  scapulae,  the  latter 
being  dorsal  to  the  former. 

In  front  of  the  anterior  trapezius  on  the  side  of  the  neck  is 
the  sternomastoid  muscle,  whose  function  is  to  turn  and  depress 
the  head;  it  extends  from  the  skull  back  of  the  external  ear 
to  the  breastbone. 

On  the  side  of  the  head  are  two  prominent  muscles,  the 
masseter  and  the  temporal,  whose  function  is  to  close  the  lower 
jaw.  The  former  lies  below  and  back  of  the  eye  ;  the  latter  is  a 
large  fan-shaped  muscle  which  covers  the  side  and  top  of  the 
head  back  of  and  above  the  eye,  and  extends  to  the  lower  jaw. 

On  the  proximal  division  of  the  fore  leg  are  seen  two  large 
muscles,  the  lateral. and  the  intermediate  portions  of  the  triceps; 
they  are  inserted  by  a  broad  tendon  in  the  olecranon  process  of 
the  ulna.  The  intermediate  portion  extends  from  the  scapula 
and  forms  the  hinder  border  of  the  upper  arm ;  the  lateral  por- 
tion extends  from  the  proximal  end  of  the  huinerus  and  forms 
its  lateral  surface. 

On  the  proximal  division  (the  thigh)  of  the  hind  leg  are  seen 
the  sartorius  muscle,  which  forms  its  anterior  border,  and  the 
biceps  femoris,  a  large  muscle  which  forms  its  middle  and  hinder 
portion.  Between  them  is  the  membranous  fascia  lata. 

Exercise  47.  Draw  the  lateral  aspect  of  the  animal  and  place  in 
it  the  outlines  of  these  muscles,  showing  the  direction  of 
their  fibers.  Carefully  label  all. 

Study  the  muscles  of  the  ventral  aspect  of  the  trunk  and  legs. 
Covering  the  abdomen  are  the  paired  external  oblique  muscles,  which 
have  already  been  described.  In  the  region  of  the  breast  are  the 
pectoral  muscles.  These  constitute  a  group  of  four  large  muscles, 
more  or  less  connected  with  one  another,  which  extend  from 
the  sternum  to  the  humerus  and  pull  the  fore  legs  backward 
and  medially.  In  front  of  the  anterior  pectoral  is  the  clavobrachial, 
which  we  have  already  seen ;  its  dorsal  continuation,  the  clavo- 
trapezius,  appears  on  the  side  of  the  neck.  Medial  to  the  last- 
named  muscle  is  the  sternomastoid. 


268  VERTEBEATE  ZOOLOGY 

On  the  upper  arm  the  posterior  border  is  formed  by  the  inter- 
mediate portion  of  the  triceps;  the  ventral  portion  is  formed 
by  the  biceps  brachii,  which  extends  from  the  scapula  to  the 
humerus. 

On  the  hind  leg  two  prominent  muscles  appear  on  the  inner 
side  of  the  thigh,  —  the  sartorius  which  forms  its  anterior  and  the 
gracilis  which  forms  its  posterior  portion. 

Exercise  48.  Draw  the  ventral  aspect  of  the  trunk  and  place  in 
it  outlines  of  these  muscles,  showing  the  direction  of  their 
fibers.  Carefully  label  all. 

Beginning  with. those  of  the  hind  legs,  .dissect  out  each  of 
the  muscles  that  has  been  observed ;  completely  free  it  from 
the  abutting  organs  and  find  its  origin  and  insertion.  Do  not, 
however,  disarticulate  or  injure  any  of  the  bones.  While  study- 
ing the  external  oblique  muscle  note  that  the  abdominal  wall  is 
composed  of  the  following  muscles  :  the  external  oblique  on  the 
outside ;  the  internal  oblique  just  beneath  it,  the  fibers  of  which 
run  at  right  angles  to  the  fibers  of  the  external  oblique ;  the 
rectus  abdominis,  a  long  narrow  muscle  which,  with  its  fellow, 
extends  in  the  midventral  area  from  the  pubis  to  the  ribs,  and 
lies  between  the  aponeurosis  of  the  two  obliques  anteriorly  and 
dorsal  to  both  posteriorly ;  and  the  transversus  muscle,  which  lies 
next  to  the  abdominal  cavity,  the  fibers  of  which  have  a  trans- 
verse direction. 

The  skeletal  system.  This  is  made  up  of  two  portions,  —  the 
exoskeleton  and  the  endoskeleton.  The  former  consists  of  certain 
special  integumental  structures,  —  the  hair,  claws,  and  teeth. 
The  hairs  are  epidermal  structures  which  form  a  protective  cov- 
ering against  cold  and  external  injuries.  They  are  also  to  a  cer- 
tain extent  tactile  organs.  The  whiskers,  or  vibrissae,  are  enlarged 
hairs,  the  principal  function  of  which  is  sensory.  The  claws  are 
horny  epidermal  structures  and  are  closely  allied  to  hairs.  The 
teeth  have  a  twofold  origin :  the  dentine  is  a  dermal  structure, 
being  modified  dermal  bone,  and  the  enamel  an  epidermal  struc- 
ture, arising  as  a  secretion  of  epidermal  cells. 


THE  CAT  269 

The  endoskeleton  is  the  bony  and  cartilaginous  framework  of 
the  body.  It  may  be  divided  into  the  axial  skeleton,  which 
includes  the  skull  and  the  vertebral  column,  together  with  the 
ribs  and  the  sternum,  and  the  appendicular  skeleton,  which  includes 
the  framework  of  the  extremities. 

To  prepare  the  internal  skeleton  for  study,  open  the  abdomi- 
nal cavity,  without  injuring  the  sternum  or  ribs,  and  remove 
all  the  viscera.  Cut  away  the  diaphragm  and  remove  the  heart 
and  lungs  and  other  thoracic  organs.  Remove  the  greater  part 
of  the  muscles  which  still  remain  in  the  body,  being  very  care- 
ful not  to  injure  the  bones. 

The  body,  thus  prepared,  should  be  boiled  until  the  bones  can 
be  thoroughly  cleaned.  It  is  well  while  doing  this  to  disarticu- 
late the  head  and  the  hind  limbs  from  the  remainder  of  the 
skeleton.  Do  not,  however,  boil  the  bones  until  the  ligaments 
are  destroyed  and  the  bones  fall  apart.  It  is  also  well  to  pass  a 
string  through  the  neural  canal  as  soon  as  the  spinal  cord  is 
destroyed,  and  tie  the  two  ends  together  so  as  not  to  lose  the 
sequence  of  the  vertebrae,  and  to  number  the  ribs. 

The  appendicular  skeleton.  The  anterior  extremities  are  made 
up  of  the  pectoral  girdle  and  the  fore  legs.  The  pectoral  girdle 
is  a  paired  structure  which  in  most  land  vertebrates  is  made  up, 
on  each  side,  of  the  scapula,  coracoid,  and  procoracoid  or  clavicle. 
In  the  cat  it  is  very  incomplete,  the  dorsal  element,  the  scapula, 
being  the  only  one  which  is  well  represented.  This  is  a  flat, 
triangular  bone,  which  lies  between  the  muscles  and  the  ribs 
near  the  anterior  end  of  the  thorax,  on  each  side.  Projecting 
from  the  middle  of  the  lateral  surface  is  a  flat  ridge  called  the 
spine  of  the  scapula,  which  divides  this  surface  into  two  areas,  — 
the  supraspinous  fossa  which  lies  anterior  and  the  infraspinous  fossa 
which  lies  posterior  to  the  spine.  Ventrally  the  spine  bears  two 
processes,  —  the  acromion  process  near  the  ventral  end  and  the 
metacromion  process  dorsal  to  it.  At  the  ventral  end  of  the  scap- 
ula is  a  depression  called  the  glenoid  fossa,  in  which  the  humerus 
articulates.  Near  the  anterior  end  of  this  fossa  is  a  curved  pro- 
jection, the  coracoid  process,  which  is  homologous  to  the  coracoid 
bone  of  the  lower  vertebrates. 


270  VERTEBRATE  ZOOLOGY 

Besides  the  scapula  the  pectoral  girdle  contains,  on  each  side, 
the  clavicle.  This  is  a  small  curved  bone  which  lies  imbedded  in 
the  muscles  of  the  shoulder.  It  does  not  articulate  with  any  other 
bone  but  is  joined  with  the  acromion  process  by  a  ligament. 

Exercise  49.  Draw  the  lateral  side  of  the  scapula. 

The  skeleton  of  the  fore  leg  is  made  up  of  three  divisions,  —  a 
proximal,  a  middle,  and  a  distal  division.  The  proximal  division 
is  formed  of  the  humerus,  a  large  cylindrical  bone.  At  its  upper 
end  are  two  prominences,  of  which  the  outer  one  is  the  greater 
tuberosity  and  the  inner  is  the  lesser  tuberosity  of  the  humerus. 
Along  the  anterior  side  near  its  upper  end  is  an  elevation  called 
the  deltoid  ridge.  Near  the  lower  end  is  an  opening  in  the  bone, 
—  the  supracondyloid  foramen ;  and  a  deep  depression  —  the  olecra- 
non  fossa  —  is  present  on  the  hinder  side. 

The  middle  division  of  the  leg  is  formed  of  the  radius  and  the 
ulna,  which  articulate  with  the  distal  end  of  the  humerus.  The 
ulna  is  the  hindermost  and  the  larger  of  the  two  bones,  and 
possesses  at  its  proximal  end  the  large  olecranon  process  which 
articulates  in  the  olecranon  fossa  of  the  humerus  and  forms  the 
elbow.  The  articular  surface  of  the  ulna  with  the  humerus 
is  formed  by  the  semilunar  notch,  a  deep  depression  just  back  of 
the  olecranon  process.  The  radius  is  preaxial  in  position,  being 
in  front  of  the  ulna.  Note  carefully  its  relation  to  the  ulna 
and  to  the  bones  it  articulates  with  at  both  ends. 

The  distal  division  of  the  fore  leg  is  formed  by  the  carpus  or 
wrist  and  the  manus  or  hand.  The  carpal  bones  are  seven  in 
number,  arranged  in  two  rows,  three  being  in  the  proximal  and 
four  in  the  distal  row.  The  hand  is  composed  of  the  metacarpal 
bones  and  the  digits.  The  metacarpals  are  five  in  number,  of 
which  the  first  is  the  shortest.  The  digits  also  number  five, 
each  one  being  composed  of  a  number  of  bones  called  phalanges. 
The  first  digit,  which  corresponds  to  the  thumb,  is  composed 
of  two  phalanges ;  the  others  have  three  apiece. 

Exercise  so.  Make  a  drawing  showing  all  the  bones  of  the  leg. 
Carefully  label  all. 


THE  CAT  271 

The  posterior  extremities  are  made  up  of  the  pelvic  girdle,  or 
pelvis,  and  the  hind  legs.  The  pelvic  girdle  is  formed  by  two 
bones,  the  right  and  left  innominate  bones,  which  together  form  an 
arch.  This  arch  articulates  dorsally  with  a  portion  of  the  spinal 
column  called  the  sacrum;  ventrally  the  two  innominate  bones 
meet  and  unite  in  the  midventral  line,  this  union  being  called 
the  symphysis  pubis..  In  the  middle  of  the  lateral  surface  of  each 
innominate  bone  is  a  circular  depression,  called  the  acetabulum, 
in  which  the  femur  articulates.  A  large  hole,  called  the  obturator 
foramen,  is  present  in  the  ventral  half  of  the  bone.  The  innom- 
inate bone  is  formed  by  the  union  of  four  bones,  —  the  ilium 
which  forms  its  dorsal  portion,  the  ischium  and  pubis  which  form 
its  ventral,  and  the  acetabular,  a  small  bone  between  the  ®ther 
three,  which  forms  a  part  of  the  acetabulum.  The  ilium  articu- 
lates with  the  sacrum ;  the  ischium  and  the  pubis  are  sepa- 
rated by  the  obturator  foramen,  the  former  being  the  larger 
and  more  posterior  of  the  two.  In  most  land  vertebrates  the 
pelvic  girdle  is  composed  of  three  bones,  —  the  ilium,  pubis, 
and  ischium. 

Exercise  51.  Make  a  drawing  of  the  lateral  aspect  of  the  innom- 
inate bone. 

The  skeleton  of  the  hind  leg  may  be  divided  into  a  proximal, 
a  middle,  and  a  distal  division.  The  femur  or  thigh  bone  forms 
the  proximal  division  ;  it  is  a  cylindrical  bone,  at  the  upper  end  of 
which  is  the  head,  which  articulates  in  the  acetabulum.  At  the 
side  of  the  head  is  a  large  protuberance  called  the  great  trochanter ; 
distally  the  bone  ends  in  two  projections,  —  the  condyles. 

On  the  anterior  side  of  the  distal  end  of  the  femur  is  a  small 
independent  membrane  bone  which  develops  in  a  tendon  and 
forms  the  kneepan ;  it  is  called  the  patella. 

The  middle  division  of  the  leg  is  formed  by  the  tibia  and  fibula. 
The  tibia  is  the  larger  and  longer  of  these  bones  and  alone 
articulates  with  the  femur.  Carefully  note  the  relation  of  these 
two  bones  with  each  other. 

The  distal  division  is  formed  by  the  tarsus  or  ankle  and  the 
pes  or  foot.  The  tarsal  bones  are  seven  in  number,  The  largest 


272  VERTEBKATE  ZOOLOGY 

is  the  calcaneum  or  heel  bone ;  the  large  bone  which  articulates 
with  the  tibia  is  the  astragalus. 

The  skeleton  of  the  foot  is  composed  of  five  metatarsal  bones 
—  of  which  the  first  is  rudimentary  —  and  four  digits  or  toes. 
Each  digit  has  three  phalanges.  The  first  digit  is  wanting;  the 
one  opposite  the  calcaneum  is  the  fifth. 

Exercise  52.  Make  a  drawing  of  the  bones  of  the  hind  leg, 
reproducing  the  outlines  of  each  exactly. 

The  axial  skeleton.  The  vertebral  column  consists  of  a  succes- 
sion of  disklike  vertebrae  which  are  closely  joined  with  one  an- 
other by  intervertebral  ligaments ;  thin  cartilaginous  disks  also 
lie  between  them.  The  column  may  be  divided  into  a  number 
of  regions,  there  being  seven  cervical,  thirteen  thoracic,  seven  lum- 
bar, three  sacral,  -and  a  variable  number  of  caudal  vertebrae. 

Each  vertebra  is  a  single  bone,  which  has  been  formed  by  the 
fusion  of  several  distinct  bones.  The  body  of  the  vertebra,  or 
centrum,  forms  its  ventral  portion.  The  neural  arch,  which  incloses 
the  neural  canal  and  is  dorsal  in  position,  is  composed  originally 
of  three  bones,  —  the  two  lateral  neural  processes  and  the  me- 
dian neural  spine  or  spinous  process.  Extending  laterally  or  ven- 
trolaterally  from  the  centrum  and  neural  process  on  each  side 
is  the  transverse  process.  Projecting  from  the  anterior  and  also 
from  the  posterior  surfaces  of  the  neural  processes  are  articular 
processes  by  which  the  vertebrae  are  firmly  fitted  together.  These 
are  the  zygapophyses.  The  anterior  or  prezygapophyses  project  at 
the  anterior  end  of  a  vertebra  and  articulate  with  the  posterior 
or  postzygapophyses  of  the  vertebra  in  front  of  it.  Between  the 
neural  processes  of  each  two  vertebrae  on  each  side  is  an  open- 
ing called  the  intervertebral  foramen,  through  which  the  spinal 
nerve  passes. 

The  cervical  vertebrae  are  not  all  alike.  The  first  two  are  called 
the  atlas  and  axis,  and  support  the  skull.  The  atlas  is  a  bony 
arch  which  consists  of  a  ventral  and  two  lateral  portions,  —  the 
latter  being  the  broad  transverse  processes.  A  centrum  and  a 
spinous  process  are  absent.  Note  the  two  surfaces  which  artic- 
ulate with  the  occipital  condyles  of  the  skull ;  note  also  the 


THE  CAT  273 

postzygapophyses.  Two  foramina  will  be  seen  on  each  side,  the 
foramen  transversarium  at  its  hinder  and  the  atlantal  foramen  at  its 
forward  end ;  note  the  groove  which  joins  them  ;  these  structures 
form  the  anterior  end  of  the  vertebrarterial  canal.  The  axis  has  a 
high  and  much  elongated  spinous  process  and  its  centrum  is  con- 
tinued anteriorly  as  a  conical  projection  called  the  odontoid  process. 
This  process  projects  into  the  atlas,  whose  centrum  it  represents, 
where  it  is  held  in  position  by  the  transverse  ligament. 

The  transverse  processes  of  the  cervical  vertebrae  are  not 
homologous  to  those  of  the  other  vertebrae,  but  each  is  equiva- 
lent to  a  transverse  process  plus  the  rudiment  of  a  rib.  Between 
this  rib-rudiment  and  the  transverse  process  is  a  round  hole,  the 
foramen  transversarium.  Note  the  shape  of  the  transverse  processes 
in  the  different  cervical  vertebrae.  The  dorsal  portion  in  each 
case  represents  the  transverse  process  proper ;  the  ventral  por- 
tion represents  the  rib-rudiment,  and  in  the  sixth  vertebra  is 
double.  In  the  seventh  vertebra  these  ribs,  and  consequently 
the  foramina  transversaria,  are  usually  absent.  The  vertebrarterial 
canal  is  formed  by  the  succession  of  the  foramina  transversaria 
on  each  side,  and  contains  the  vertebral  artery  and  vein. 

The  thoracic  vertebrae  are  distinguished  by  their  very  long  spi- 
nous processes  and  by  the  ribs  which  articulate  with  them. 
Observe  their  zygapophyses.  Thirteen  pairs  of  ribs  are  present, 
the  dorsal  portion  of  each  being  bone,  the  ventral  portion  being 
cartilage.  The  nine  anterior  pairs  of  ribs  articulate  separately 
with  the  sternum ;  the  last  three  or  four  pairs  are  united  with 
one  another  ventrally,  and  the  ventral  ends  of  the  thirteenth 
pair  are  free.  All  of  the  ribs  except  the  last  two  or  three  pairs 
articulate  dorsally  by  two  surfaces  each ;  the  capitulum,  or  head 
of  the  rib,  articulates  with  the  centrum  of  two  contiguous  ver- 
tebras, and  the  tuberculum  articulates  with  the  transverse  process. 
The  tuberculum  is  absent  on  the  last  two  or  three  ribs. 

The  sternum,  or  breastbone,  is  a  row  of  bones  which  lies  in  the 
ventral  wall  of  the  thorax  and  forms  the  ventral  support  of 
the  ribs.  The  foremost  of  these  bones  is  the  manubrium ;  the 
hindermost  is  the  ensiform  process,  the  posterior  part  of  which  is 
cartilaginous. 


274  VEETEBKATE  ZOOLOGY 

The  lumbar  vertebrae  are  larger  than  the  thoracic ;  they  are  dis- 
tinguished by  the  large  size  of  the  transverse  processes,  which 
are  directed  backward  and  downward. 

The  sacral  vertebrae  in  the  adult  form  a  single  bone  called  the 
sacrum.  The  two  innominate  bones  which  form  the  pelvis  are 
closely  joined  with  it.  Note  the  two  intervertebral  foramina  on 
each  side  of  it. 

The  caudal  vertebrae  become  gradually  smaller  toward  the 
hinder  end,  the  last  ones  consisting  of  centra  only.  A  number 
of  caudal  vertebrae  near  the  forward  end  of  the  tail  bear  each 
a  pair  of  short  ventral  processes  called  the  haemal  processes ;  the 
space  between  the  two  members  of  each  pair  is  closed  by  a  small 
median  chevron  bone  and  contains  the  caudal  artery  and  vein. 

Exercise  53.  Draw  the  following  views :  the  anterior  end  of  the 
atlas,  the  lateral  aspect  of  the  axis,  and  the  anterior  end  of 
the  sixth  cervical  vertebra,  on  a  scale  of  2  or  3. 

Exercise  54.  Draw  the  anterior  end  of  the  fourth  thoracic  verte- 
bra ;  also  the  lateral  aspect. 

Exercise  55.  Draw  the  anterior  end  and  also  the  lateral  aspect 
of  the  fourth  lumbar  vertebra. 

Exercise  56.  Draw  the  ventral  surface  of  the  sacrum. 

Exercise  57.  Draw  a  ventral  view  of  the  fourth  caudal  vertebra ; 
also  one  of  the  last  caudal  vertebra. 

The  skull.  The  skull  is  made  up  of  two  portions,  the  cranium 
and  the  visceral  skeleton.  The  former  protects  the  brain  and  the 
organs  of  special  sense,  and  the  latter  forms  the  framework  of 
the  greater  part  of  the  face,  the  jaws,  and  the  tpngue. 

Observe  the  general  character  of  the  skull.  Note  the  sutures 
by  which  the  bones  are  joined  with  one  another ;  they  are  the 
growing  surfaces,  and  in  an  old  animal  tend  to  become  obliter- 
ated by  the  fusion  of  the  bones.  Of  the  animals  studied  in  this 
course,  only  the  turtle  has  such  a  compact  and  strongly  built 
skull.  The  teeth,  although  they  are  integumentary  structures, 


THE  CAT  275 

are  sunk  into  deep  depressions  in  the  bones  of  the  jaws  and 
are  so  firmly  joined  with  them  that  a  very  solid  biting  surface 
is  formed. 

On  each  side  of  the  skull  is  the  large  orbit,  in  which  the  eye- 
ball and  its  muscles,  glands,  and  other  accessory  organs  are 
contained;  the  prominent  ridge  over  it  is  the  supraorbital  ridge. 
The  orbit  is  not  complete,  as  in  man,  but  is  open  behind  and 
at  the  side.  Just  behind  it  and  communicating  with  it  is  a 
depressed  area  called  the  temporal  fossa.  The  prominent  arch  on 
the  side  of  the  skull,  forming  the  lateral  boundary  of  the  orbit 
and  the  temporal  fossa,  is  the  zygomatic  arch.  The  large  temporal 
muscle  which  helps  to  close  the  mouth  arises  on  the  surface  of 
the  temporal  fossa. 

In  the  hinder  end  of  the  skull  is  the  foramen  magnum,  a  large 
circular  opening  through  which  the  spinal  cord  enters  the  brain 
cavity.  The  prominent  transverse  lambdoidal  ridge  marks  the  dor- 
sal border  of  the  hinder  end,  from  the  middorsal  point  of  which 
the  sagittal  ridge  runs  forward.  On  either  side  of  the  foramen 
magnum  are  the  occipital  condyles,  a  pair  of  protuberances  which 
articulate  with  the  atlas.  At  the  side  of  the  skull  just  back  of 
the  zygomatic  arch  is  the  external  auditory  meatus,  the  outer  open- 
ing of  the  ear.  At  the  anterior  end  of  the  skull  are  the  nasal 
capsules,  the  walls  of  which  are  partly  cartilaginous ;  the  openings 
in  their  forward  end  are  the  anterior  nares. 

On  the  ventral  surface  of  the  skull  on  each  side  is  the  promi- 
nent rounded  tympanic  bulla,  which  contains  the  middle  ear. 
Between  the  orbits  is  the  opening  of  the  nasopharynx.  Just  back 
of  the  incisor  teeth  are  two  large  openings,  the  foramina  incisa. 
Note  the  articulation  of  the  lower  jaw. 

Study  the  bones  of  the  skull  as  they  appear  on  the  dorsal, 
the  lateral,  and  the  ventral  surfaces. 

The  bones  of  the  cranium,  as  already  suggested,  fall  into  two 
categories,  —  those  of  the  cranium  proper,  or  brain  case,  and  those 
of  the  special  sense  capsules.  Those  belonging  to  the  brain  case 
occupy  the  central  portions  of  the  skull.  The  organs  of  hear- 
ing, sight,  and  smell  are  lodged,  in  the  embryo,  in  protective 
membranous  or  cartilaginous  capsules ;  in  the  adult,  certain 


276  VEBTEBKATE  ZOOLOGY 

bones  have  developed  in  these  capsules,  which  form  an  intimate 
union  with  the  brain  case.  The  auditory  capsule  has  undergone 
the  most  complete  ossification,  the  bones  present  in  the  adult 
forming  the  side  of  the  skull  back  of  the  orbits.  The  optic 
capsule  does  not  ossify,  but  a  membrane  bone,  the  lachrymal, 
appears  at  its  anterior  end.  The  orbit,  in  which  the  eye  lies,  is 
formed  of  the  bones  of  the  brain  case  and  the  visceral  skeleton. 
The  nasal  capsules  are  bony  and  cartilaginous,  and  form  the 
forward  end  of  the  skull. 

The  bones  of  the  visceral  skeleton  fall  readily  into  three  cate- 
gories, according  to  their  position,  —  those  of  the  upper  jaw 
and  upper  part  of  the  face,  those  of  the  lower  jaw,  and  those 
of  the  tongue. 

The  dorsal  and  posterior  aspects.  The  hinder  end  of  the  skull 
is  formed  of  a  single  bone,  the  occipital,  which  has  been  formed 
by  the  fusion  of  four  bones,  —  the  ventral  basioccipital,  the  two 
exoccipitals  which  bear  the  two  occipital  condyles,  and  the  dorsal 
supraoccipital. 

In  the  dorsal  aspect  the  small  interparietal  bone  forms  the 
median  portion  of  the  lambdoidal  ridge.  In  front  of  this  ridge 
are  the  large  paired  parietal  bones,  and  in  front  of  them  the  large 
paired  frontal  and  the  paired  nasal  bones,  the  latter  lying  at  the 
anterior  end  of  the  skull.  These  bones  are  all  membrane  bones 
and  form  the  roof  of  the  skull. 

Lateral  to  each  parietal  is  the  large  temporal  bone  which  con- 
tains the  auditory  organ.  Projecting  forward  from  it  is  the 
large  zygomatic  process  which  forms  the  hinder  part  of  the 
zygomatic  arch. 

On  each  side  of  the  nasals  is  the  maxillary  bone,  and  in  front 
of  them  are  the  two  intermaxillary  bones;  these  two  pairs  of 
bones  bear  the  teeth.  Projecting  backward  from  the  maxillary 
on  each  side  is  its  zygomatic  process,  which  forms  the  anterior 
portion  of  the  zygomatic  arch.  The  middle  portion  of  the  arch 
is  formed  by  the  malar  bone.  Extending  from  this  bone  medially 
and  dorsally  is  its  frontal  process,  which  almost  meets  the  zygo- 
matic process  of  the  frontal  bone,  and  separates  the  orbit  from 
the  temporal  fossa. 


THE  CAT  277 

Between  the  maxillary  and  frontal  bones  in  the  orbit  is  the 
small  lachrymal  bone. 

Exercise  58.  Draw  a  view  of  the  dorsal  aspect  of  the  skull,  with 
the  outlines  of  the  bones  which  appear. 

The  lateral  aspect.  The  temporal  bone  is  here  seen  in  its  entire 
extent.  It  is  made  up  of  three  principal  portions,  —  a  dorsal 
expanded  squamous  portion,  which  bears  the  zygomatic  process; 
a  tympanic  portion,  which  forms  the  tympanic  bulla,  and  in  which 
is  the  external  auditory  meatus ;  and  a  petrous  portion,  which  is 
the  hinder  and  inner  part  and  contains  the  inner  ear.  Just  back 
of  the  external  auditory  meatus  is  the  stylomastoid  foramen,  for 
the  passage  of  the  facial  nerve,  beneath  which  is  a  deep  pit 
resembling  a  foramen.  Just  in  front  of  this  foramen  are  four 
foramina  in  a  row,  the  one  nearest  it  being  the  foramen  ovale,  for 
the  passage  of  the  mandibular  branch  of  the  trigeminal  nerve; 
the  next  one,  the  foramen  rotundum,  for  the  passage  of  the  max- 
illary branch  of  the  trigeminal;  the  next,  the  orbital  fissure,  for 
the  passage  of  the  oculomotor,  trochlear,  and  abducens  nerves, 
and  the  ophthalmic  branch  of  the  trigeminal ;  and  the  anterior 
one,  the  optic  foramen,  for  the  passage  of  the  optic  nerve. 

In  the  anterior  margin  of  the  orbit  are  two  foramina,  the 
dorsal  and  smaller  one  being  the  lachrymal  foramen,  through 
which  the  nasolachrymal  duct  passes  to  the  nose ;  the  ventral 
one  being  the  infraorbital  foramen,  through  which  an  artery  and 
a  branch  of  the  maxillary  nerve  pass  from  the  orbit  to  the  face. 
A  short  distance  back  of  these  are  two  foramina  close  together, 
—  the  sphenopalatine  foramen,  the  larger  one,  and  the  palatine  fora- 
men, through  which  small  arteries  and  nerves  pass. 

Exercise  59.  Draw  a  view  of  the  lateral  aspect. 

The  ventral  aspect.  In  front  of  the  occipital  is  the  basisphe- 
noid  bone,  and  in  front  of  that  the  small  presphenoid.  The  paired 
lateral  projections  of  the  former  are  homologous  to  the  alisphe- 
noids  of  lower  vertebrates ;  a  pair  of  processes  projecting  ven- 
trally  in  front  of  these  are  the  pterygoid  processes,  which  are 
homologous  to  the  parasphenoid  bone  of  lower  vertebrates.  The 


278  VEKTEBKATE  ZOOLOGY 

paired  lateral  projections  of  the  presphenoid  are  homologous 
to  orbitosphenoid  bones.  In  front  of  the  presphenoid  are  the 
paired  palatine  bones,  which  form  the  hard  palate.  In  the  base 
of  the  zygomatic  process  of  the  temporal  bone  is  the  glenoid 
cavity,  in  which  the  lower  jaw  articulates. 

In  addition  to  the  foramina  already  mentioned  the  large 
foramen  jugale  and  the  hypoglossal  foramen  will  be  seen.  The  for- 
mer is  a  large  hole  between  the.  tympanic  bulla  and  the  occip- 
ital bone  through  which  the  glossopharyngeal,  vagus,  and  spinal 
accessory  nerves  pass ;  the  latter  is  in  the  hinder  margin  of 
the  former. 

Exercise  60.  Draw  a  view  of  the  ventral  aspect. 

With  a  fine  saw  divide  the  skull  into  two  slightly  unequal 
halves  by  a  longitudinal  dorsoventral  incision  just  at  one  side 
of  the  median  line,  and  study  its  inner  surface.  The  interior 
of  the  skull  is  divided  into  three  cavities,  —  the  cranial,  the 
auditory,  and  the  nasal  cavities,  which  contain  the  brain,  the 
auditory,  and  the  olfactory  organs,  respectively. 

The  cranial  cavity  is  further  subdivided  into  the  cerebellar,  cerebral, 
and  olfactory  fossae.  The  first  of  these  occupies  the  hinder  part  of 
the  skull,  being  bounded  anteriorly  by  the  tentorium,  the  trans- 
verse partition  extending  inward  from  the  parietal  bones.  In 
the  floor  of  this  cavity  is  the  internal  auditory  meatus,  a  large 
depression  divided  by  a  partition  into  two  parts,  the  dorsal  part 
containing  the  foramen  of  the  facial  nerve,  the  ventral  part 
containing  a  number  of  small  foramina  of  the  auditory  nerve. 
Beneath  this  meatus  is  the  hypoglossal  foramen,  posterior  to  which 
is  the  condyloid  canal,  through  which  a  vein  passes. 

The  cerebral  fossa  is  the  largest  of  the  three ;  it  occupies  the 
entire  central  portion  of  the  cranial  cavity.  In  its  floor  is  the 
large  optic  foramen,  just  back  of  which  is  a  large  circular  depres- 
sion, the  sella  turcica,  in  which  the  hypophysis  lies. 

The  olfactory  fossa  occupies  the  anterior  end  of  the  cranial 
cavity  and  lies  beneath  the  frontal  bones.  Its  anterior  end  is 
bounded  by  the  ethmoid  bone,  in  which  the  mesethmoid  portion,  the 
labyrinths,  and  the  cribriform  plate  may  be  distinguished.  The 


THE  CAT  279 

mesethmoid,  the  median  portion,  is  a  vertical  plate  which  sep- 
arates the  nasal  capsules  from  each  other;  the  cribriform  plate 
is  a  transverse  perforated  bone  which  forms  the  anterior  wall  of 
the  brain  cavity  and  gives  passage  to  the  fibers  of  the  olfactory 
nerve  into  the  nasal  capsules;  the  labyrinths  are  folded  bony 
plates  which  are  attached  to  the  cribriform  plate  on  each  side 
and  form  the  turbinals  of  the  nasal  capsules. 

The  nasal  cavity  occupies  the  anterior  end  of  the  skull.  It 
is  divided  into  a  right  and  a  left  nasal  cavity  by  the  vertical 
mesethmoid  bone,  while  the  hinder  wall  is  formed  by  the  cribri- 
form plate.  The  floor  of  the  nasal  cavities  is  formed  by  the 
paired  palatine  bones  and  its  roof  by  the  paired  nasal  bones.  The 
vomer  is  a  narrow  bone  which  lies  along  the  ventral  edge  of 
the  mesethmoid  and  helps  form  the  nasal  septum.  The  hinder 
part  of  each  cavity  is  divided  by  a  horizontal  ridge  of  the  vomer 
into  a  dorsal  and  a  ventral  compartment.  The  latter  is  the 
smaller  and  is  the  respiratory  part  of  the  nose;  the  former  is 
the  olfactory  part.  Note  the  anterior  and  posterior  nares. 

The  auditory  cavity  of  the  skull  has  already  been  studied. 

Note  the  frontal  and  the  sphenoidal  sinuses,  open  spaces  in  the 
frontal  and  presphenoid  bones;  they  communicate  with  the 
nasal  cavity. 

Exercise  61.  Draw  a  view  of  the  section  of  the  skull  showing 
these  cavities  and  the  boundaries  of  the  bones  forming 
them. 

Of  the  bones  just  studied,  the  following  belong  to  the  cranium 
proper,  or  brain  case:  the  occipital,  basisphenoid,  presphenoid, 
and  ethmoid,  all  of  which  are  cartilage  bones  and  form  its  base ; 
and  the  parietals  and  frontals,  which  are  membrane  bones  and 
form  its  roof.  The  special  sense  capsules  are  three  in  number. 
The  auditory  capsule  is  lodged  in  the  temporal  bone.  As  we  have 
seen,  this  bone  is  made  up  of  three  parts,  —  the  petrous,  tym- 
panic, and  squamous  portions.  The  petrous  part,  which  con- 
tains the  inner  ear  and  is  a  cartilage  bone,  is  formed  by  a 
fusion  of  the  prootic,  epiotic,  and  opisthotic  bones,  —  these  bones 
being  in  many  lower  vertebrates  distinct  and  separate.  The 


280  VEKTEBKATE  ZOOLOGY 

tympanic  portion,  which  contains  the  middle  ear,  is  a  mem- 
brane bone.  The  squamosal  is  also  a  membrane  bone ;  it  forms 
a  part  of  the  wall  of  the  brain  case.  The  optic  capsule  does  not 
ossify,  but  the  lachrymal  is  a  membrane  bone  which  develops 
in  connection  with  it.  The  nasal  capsule  is  formed  by  the  eth- 
moid, the  nasals,  and  the  vomer,  —  the  ethmoid  alone  being  a 
cartilage  bone. 

The  bones  of  the  visceral  skeleton  which  enter  into  the  forma- 
tion of  the  upper  jaw  and  the  upper  part  of  the  face  are  the 
maxillaries,  premaxillaries,  malars,  and  palatines. 

The  lower  jaw,  or  mandible,  is  a  single  bone  which  is  composed 
of  a  right  and  a  left  half,  joined  in  the  median  line.  At  the 
proximal  end  of  each  half  are  the  condyle,  which  articulates  in 
the  glenoid  cavity  of  the  temporal  bone,  and  the  coronoid  process, 
which  projects  dorsally  and  in  which  the  temporal  muscle  is 
inserted.  Just  in  front  of  the  condyle  is  the  inferior  dental  foramen, 
through  which  a  branch  of  the  mandibular  nerve  enters  the  bone. 

Exercise  62.  Draw  a  view  of  the  medial  aspect  of  the  mandible. 
The  hyoid  apparatus  has  already  been  studied  (see  page  245). 


INDEX 


Abdominal  cavity  •  dogfish,  4 ;  perch, 
37  ;  Necturus,  69 ;  frog,  99 ;  turtle, 
139;  pigeon,  174;  cat,  219-221. 

Abdominal  pores :  dogfish,  3. 

Acetabulum  :  Necturus,  86 ;  frog,  128 ; 
turtle,  157  ;  pigeon,  203;  cat,  271. 

Adrenal  body  :  frog,  105 ;  turtle,  146 ; 
pigeon,  178 ;  cat,  228. 

Air  bladder :  perch,  37. 

Air  sac :  see  Sac,  air. 

Ala  spuria  :  pigeon,  171. 

Alar  membrane  :  pigeon,  172. 

Amphibians,  65. 

Ampulla  of  ear:  dogfish,  15;  perch, 
45 ;  Necturus,  74. 

Ankle :  see  Tarsus. 

Anterior  commissure :  cat,  262. 

Anterior  cornua:  frog,  131;  pigeon, 
212 ;  cat,  245. 

Anterior  extremities:  Necturus,  83; 
frog,  125 ;  turtle,  156 ;  pigeon, 
201 ;  cat,  269. 

Anterior  nares  :  see  Nostrils. 

Anuran  amphibian :  94. 

Anus:  dogfish,  3;  perch,  35;  Necturus, 
67  ;  frog,  96  ;  turtle,  137  ;  pigeon, 
170 ;  cat,  216,  223. 

Anvil :  see  Incus. 

Aorta:  dogfish,  23,  24 ;  perch,  51,  53; 
Necturus,  80,  81 ;  frog,  120 ;  turtle, 
141 ;  pigeon,  180;  cat,  233,  236. 
abdominal :  cat,  233. 
dorsal:  dogfish,  23,  24;  perch,  51, 
53 ;  Necturus,  81 ;  frog,  120 ;  tur- 
tle, 163 ;  pigeon,  180,  183. 
left:  turtle,  141,  162. 
right:  turtle,  141,  162. 
thoracic :  cat,  236. 
ventral :    dogfish,    23 ;    perch,    51 ; 
Necturus,  80. 

281 


Aorta  ascendens :  see  Aorta,  ventral. 
Aorta  descendens :  see  Aorta,  dorsal. 
Aponeurosis:  frog,  122. 
Appendages:  dogfish,  3;   perch,  35; 
Necturus,   67;    frog,    96;    turtle, 
137 ;  pigeon,  170 ;  cat,  217. 
Appendicular   skeleton:  dogfish,   27, 
31;  perch,  55,  63;  Necturus,  83; 
frog,  125;  turtle,  149,  156;  pigeon, 
201 ;  cat,  269. 

Aqueductus  Sylvii:  dogfish,  20;  perch, 
48;    Necturus,    77;    frog,    114; 
pigeon,  197;  cat,  263. 
Aqueous  humor :  dogfish,  15 ;  perch, 

44;  pigeon,  193;  cat,  256. 
Arachnoid :  cat,  257. 
Arbor  vitse  :  cat,  263. 
Arch,  aortic :  frog,  101,  120. 

branchial:   dogfish,  30,  31;  perch, 

57,  60 ;  Necturus,  88. 
carotid:  frog,  101,  120. 
gill :  see  Arch,  branchial, 
hssmal:  dogfish,  25,  28;  perch,  54, 

55 ;  Necturus,  93. 
hyoid:  dogfish,  30;  perch,  57,  59; 

Necturus,  88. 

mandibular :  dogfish,  30;  perch,  57, 58. 
neural:  dogfish,  25,  27;  perch,  54, 
55 ;  Necturus,  92 ;  frog,  129 ;  tur- 
tle, 151 ;  pigeon,  205 ;  cat,  272. 
pulmocutaneous :  frog,  101,  120. 
systemic:  frog,  101,  120. 
visceral :  dogfish,  30 ;  perch,  57. 
zygomatic :  cat,  275. 
Area  elliptica :  cat,  261. 
Area  ovalis :  cat,  261. 
Arteries:  dogfish,  20,  23;  perch,  49, 
51,   53;   Necturus,   77,   80;   frog, 
114,  120;  turtle,  158,  161;  pigeon, 
175,  180,  183 ;  cat,  225,  233,  236. 


282 


VEBTEBRATE  ZOOLOGY 


Artery,  adrenolumbar :  cat,  233. 
afferent    branchial :     dogfish,     23 ; 

perch,  51 ;  Necturus,  80. 
anterior    mesenteric  :   dogfish,   24 ; 

frog,    121 ;    turtle,    162 ;   pigeon, 

183 ;  cat,  233. 

anterior  renal :  pigeon,  184. 
axillary :  turtle,  141,  162 ;  cat,  240. 
basilar :  cat,  239. 
brachial:  turtle,  141,  162;  pigeon, 

180 ;  cat,  236. 
bronchial :  cat,  237. 
carotid :  perch,  51 ;  Necturus,  81 ; 

frog,  120;  turtle,  141, 162;  pigeon, 

180 ;  cat,  236. 
caudal :     dogfish,    24  ;    perch,    51 ; 

Necturus,  81 ;   pigeon,  184  ;   cat, 

234. 

cervical :  pigeon,  180. 
cceliac :    dogfish,    24 ;    perch,    51 ; 

frog,    121 ;    turtle,   162  ;    pigeon, 

183 ;  cat,  233. 
eoeliaco-mesenteric  :    Necturus,  81 ; 

frog,  121. 

common  iliac :  frog,  121 ;  turtle,  163. 
coronary :  cat,  236. 
costocervical :  cat,  239. 
cutaneous :  Necturus,  81 ;  frog,  120. 
deep  femoral :  cat,  234. 
efferent    branchial :     dogfish,    23 ; 

perch,  51 ;  Necturus,  80. 
epigastric :  turtle,  163 ;  cat,  234. 
external  carotid :  Necturus,  81 ;  frog, 

120;  pigeon,  181. 
external  iliac :  frog,  121;  turtle,  163 ; 

cat,  234. 

external  maxillary :  cat,  240. 
femoral :    frog,    121 ;    pigeon,   184  ; 

cat,  234. 

gastric :  Necturus,  81. 
gastrica  sinistra  :  cat,  233. 
gastroduodenal :  turtle,  163. 
genital :  Necturus,  81 ;  frog,  121. 
hepatic :  cat,  233. 
hypogastric :    see  Artery,    internal 

iliac, 
iliac :  dogfish,  25 ;  Necturus,  81 ;  frog, 

121 ;  turtle,  163 ;  pigeon,  163 ;  cat, 

234. 


Artery,  iliolumbar :  cat,  234. 

inferior  mesenteric  :  see  Artery,  pos- 
terior mesenteric. 
innominate  :  turtle,  141, 161;  pigeon, 

180 ;  cat,  236. 
intercostal :  cat,  237. 
internal  carotid :  Necturus,  81 ;  frog, 

120;  pigeon,  181. 
internal  iliac :  frog,  121 ;  turtle,  163 ; 

pigeon,  184 ;  cat,  234. 
internal    mammary :     turtle,    162 ; 

pigeon,  180 ;  cat,  233. 
laryngeal:  frog,  121. 
lateral :  dogfish,  24. 
left  carotid :  turtle,  141, 162 ;  cat,  236. 
left  pulmonary  :  turtle,  141, 162  ;  cat, 

236. 
lef t  subclavian  :  turtle,  141, 162 ;  cat, 

236. 

lingual :  cat,  240. 
lumbar :  frog,  121 ;  cat,  234. 
mediastinal :  cat,  236. 
muscularis:  cat,  240. 
occipito-vertebral :  frog,  121. 
cesophageal:  frog,  121. 
ovarian :  cat,  233. 
pectoral :  pigeon,  180. 
phrenic :  cat,  233. 
posterior  auricular :  cat,  240. 
posterior  mesenteric  :    dogfish,  24 ; 

Necturus,  81;  frog,  121;  pigeon, 

184 ;  cat,  233. 
pulmonary  :  Necturus,  81 ;  frog,  120 ; 

turtle,  141,  162 ;  pigeon,  175,  181 ; 

cat,  225,  233,  236. 
renal :  dogfish,  25 ;  Necturus,  81 ;  cat, 

233. 
right  carotid :  turtle,  141,  162 ;  cat, 

236,  240. 
right  pulmonary :  turtle,  141,  162 ; 

cat,  236. 
right  subclavian:  turtle,  141,  161; 

cat,  236,  239. 

sacralis  media :  see  Artery,  caudal. 
sciatic :  frog,  122 ;  turtle,  163 ;  pigeon, 

184. 

spermatic :  cat,  233. 
spinal :  dogfish,  24 ;  perch,  51 ;  Nec- 
turus, 81. 


INDEX 


283 


Artery,  splenic  :  cat,  221,  233. 
subclavian :  dogfish,  24 ;  perch,  51 ; 
Necturus,    81 ;    frog,     121 ;    tur- 
tle,  141,  162;   pigeon,    180;  cat, 
236. 

subscapular :  cat,  240. 
superior  mesenteric  :  see  Artery,  an- 
terior mesenteric. 
systemic  :  pigeon,  175 ;  cat,  226. 
temporal :  cat,  240. 
thyroid :  cat,  240. 
urogenital :  frog,  121. 
vertebral:   frog,  121;   pigeon,  180; 

cat,  239. 

Ascending  colon :  cat,  222. 
Astragalus :  frog,  128 ;  turtle,  157 ;  cat, 

272. 
Atlas :  Necturus,  92 ;  frog,  129 ;  turtle, 

15.1 ;  pigeon,  206  ;  cat,  272. 
Auditory  capsule :  dogfish,  28 ;  perch, 
62 ;  Necturus,  90 ;  frog,  133 ;  turtle, 
156 ;  pigeon,  211 ;  cat,  279. 
Auditory  organs :  see  Ear. 
Auricle :    dogfish,   6 ;    perch,  38,   50 ; 
Necturus,   69 ;  frog,  101 ;  turtle, 
140;  pigeon,  175,  179;  cat,  235. 
Auricular  appendix :  cat,  235. 
Auricular  septum  :  cat,  241. 
Auriculo-ventricular  opening :  dogfish, 
7;  perch,  50;  frog,  103;  pigeon, 
184,  185 ;  cat,  241. 

Axial  skeleton :  dogfish,  27 ;  perch, 
55;  Necturus,  83,  87;  frog,  125, 
129 ;  turtle,  149 ;  pigeon,  201,  204 ; 
cat,  269,  272. 

Axis:  turtle,  151;  pigeon,  206;  cat, 
273. 

Barbs :  pigeon,  200. 

Barbules :  pigeon,  200. 

Basipterygium :  dogfish,  32. 

Beak :  pigeon,  168. 

Belly  of  muscles :  frog,  122. 

Birds,  166. 

Blind  spot:  dogfish,  14;  perch,  44; 
cat,  254. 

Body  cavity:  dogfish,  4;  perch,  37; 
Necturus,  69;  frog,  99;  turtle, 
139 ;  pigeon,  174  ;  cat,  219. 


Body  divisions :  dogfish,  2  ;  perch,  34 ; 

Necturus,   66;    frog,    95;    turtle, 

137 ;  pigeon,  168 ;  cat,  215. 
Body  regions :  see  Body  divisions. 
Bone,  acetabular  :  cat,  271. 

alisphenoid :  perch,  62 ;  turtle,  155. 
angular:  perch,  58;   Necturus,  87; 

frog,  131 ;  turtle,  152 ;  pigeon,  210. 
articular:    perch,   58;    turtle,    152; 

pigeon,  210. 
basal :  perch,  63,  64. 
basibranchial :  perch,  60. 
basihyal:   perch,  59;   pigeon,  212; 

cat,  245. 
basioccipital :  perch,  61;  turtle,  154; 

pigeon,  208 ;  cat,  276. 
basisphenoid :  turtle,  154;  cat,  277. 
basitemporal :  pigeon,  210. 
carpal:  turtle,  156. 
cartilage  :  perch,  57  ;  Necturus,  87 ; 

frog,  130. 

ceratobranchial :  perch,  60. 
ceratohyal :  perch,  59. 
chevron :  cat,  274. 
coronoid:  turtle,  152. 
dentary:  perch,  58;  Necturus,  87; 

frog,    131 ;    turtle,    152 ;    pigeon, 

210. 

ectopterygoid :  perch,  58. 
endopterygoid :  perch,  58. 
epibranchial :  perch,  60. 
epihyal :  perch,  59. 
epiotic:     perch,    62;    turtle,    154; 

pigeon,  211. 
ethmoid :  perch,  63 ;  frog,  132  ;  cat, 

278. 
exoccipital :    perch,  61 ;    Necturus, 

89  ;  frog,  132 ;  turtle,  154 ;  pigeon, 

208 ;  cat,  276. 
fibular:  turtle,  157. 
frontal :    perch,  62  ;    Necturus,  89 ; 

turtle,  153 ;  pigeon,  208 ;  cat,  276. 
fronto-parietal :  frog,  132. 
hyoid :  perch,  59. 
hyomandibular :  perch,  59. 
hypobranchial :  perch,  60. 
hypohyal :  perch,  59. 
innominate :  pigeon,  203 ;  cat,  271. 
interhyal :  perch,  59. 


284 


VERTEBRATE  ZOOLOGY 


Bone,  intermaxillary:  see  Bone,  pre- 

maxillary. 

intermedial :  turtle,  156. 
interuiuscular :  perch,  66. 
interopercular :  perch,  59. 
interparietal :  cat,  276. 
jugal :  turtle,  153 ;  pigeon,  210. 
lachrymal :  pigeon,  209 ;  cat,  277. 
lateral  ethmoid :  perch,  63. 
malar:  cat,  276. 
maxillary :    perch,   34 ;    frog,    134 ; 

turtle,    153;    pigeon,    210;    cat, 

276. 

median  ethmoid :  perch,  63. 
membrane  :  perch,  57, 61 ;  Necturus, 

87;  frog,  130. 

mesethmoid:  pigeon,  210;  cat,  278. 
metacarpal :  Necturus,  85 ;  frog,  127, 

129;    turtle,    157;    pigeon,    202; 

cat,  270. 

metapterygoid :  perch,  58. 
metatarsal :  Necturus,  86 ;  frog,  129 ; 

turtle,    157;    pigeon,    204;    cat, 

272. 
nasal :  perch,  62 ;  frog,  133 ;  pigeon, 

208 ;  cat,  276. 
occipital:  perch,  61;  Necturus,  89; 

frog,  132 ;  turtle,  154, 155 ;  pigeon, 

208 ;  cat,  276. 
opercular :  perch,  59. 
opisthotic :  perch,  62 ;  Necturus,  90; 

turtle,  154;  pigeon,  211. 
orbitosphenoid :  perch,  62;  pigeon, 

209. 

otic :  perch,  62. 

palatine :  perch,  58  ;  frog,  134 ;  tur- 
tle, 154  ;  pigeon,  210 ;  cat,  278. 
palatopterygoid :  Necturus,  91. 
parabasal :  see  Bone,  parasphenoid. 
paraquadrate  :  see  Bone,  squamosal. 
parasphenoid  :  perch,  63  ;  Necturus, 

90;  frog,  132. 
parietal:  perch,  62;  Necturus,  89; 

turtle,  153  ;  pigeon,  208  ;  cat,  276. 
pharyngobranchial :  perch,  60. 
pisiform :  turtle,  156 ;  cat,  217. 
postfrontal:  turtle,  153. 
posttemporal :  perch,  64. 
pref rental :  turtle,  153. 


Bone,  premaxillary  :  perch,  34  ;  Nec- 
turus, 91;  frog,  134;  turtle,  154; 
pigeon,  208 ;  cat,  276. 

preopercular :  perch,  59. 

presphenoid:  pigeon,  209;  cat, 
277. 

prootic:  perch,  62;  Necturus,  90; 
frog,  133;  turtle,  154. 

pterotic  :  perch,  62. 

pterygoid  :  frog,  134 ;  turtle,  154 ; 
pigeon,  210. 

quadrate :  perch,  58 ;  Necturus,  91 ; 
frog,  134;  turtle,  154;  pigeon, 
209. 

quadrate  j  ugal :  frog,  134;  turtle, 
153 ;  pigeon,  210. 

radial:  perch,  63,  64;  turtle,  156; 
pigeon,  203. 

sphenotic :  perch,  62. 

splenial :  Necturus,  87 ;  turtle,  152. 

squamosal:  Necturus,  91 ;  frog,  134; 
turtle,  153 ;  pigeon,  209. 

subopercular :  perch,  59. 

suborbital :  perch,  59. 

supra-angular:  turtle,  152. 

supraoccipital :  perch,  61;  turtle, 
153 ;  pigeon,  208 ;  cat,  276. 

symplectic :  perch,  59. 

temporal :  cat,  276,  277. 

ulnar :  turtle,  156 ;  pigeon,  203. 

vomer:    perch,  62;    Necturus,  90; 

frog,  133 ;  turtle,  154 ;  cat,  279. 
Bony  labyrinth :  cat,  256. 
Brain :    dogfish,    16,    19 ;    perch,   45 ; 
Necturus,  74;   frog,   109;   turtle, 
163 ;  pigeon,  188,  194 ;  cat,  257. 
Branchiostegal  membrane  :  perch,  35. 
Branchiostegal  rays  :  perch,  35,  59. 
Bronchus:   turtle,    145;   pigeon,  186; 

cat,  246. 

Bulbus  arteriosus ;  perch,  38,  50 ;  Nec- 
turus, 70. 
Bursa  of  Fabricius :  pigeon,  179. 

Csecum :  turtle,  144 ;  cat,  222,  226. 
Calcaneum  :  frog,  128  ;  cat,  272. 
Calcareous  body :  frog,  108. 
Campanula Halleri:  dogfish,  15;  perch, 
44. 


INDEX 


285 


Canal,  central :  dogfish,  19 ;  perch,  48 ; 
Necturus,  76;'  frog,  110,  114; 
pigeon,  197;  cat,  262. 

condyloid:  cat,  278. 

inguinal :  cat,  229. 

lachrymal :  cat,  252. 

mucous :  dogfish,  2,  3,  12. 

pericardio-peritoneal :  dogfish,  6. 

semicircular :  dogfish,  15;  perch,  45; 
Necturus,  73 ;  pigeon,  193 ;  cat, 
256. 

urogenital :  see  Urethra. 

vertebrarterial :    pigeon,    205;    cat, 

273. 

Capillaries:    dogfish,   20;   perch,   49; 
Necturus,  77;   frog,  114;    turtle, 
158 ;  pigeon,  175 ;  cat,  224. 
Capitulum :  pigeon,  206 ;  cat,  273. 
Caput  epididymis :  cat,  229. 
Carapace :  turtle,  136,  150. 
Carpo-metacarpus :  pigeon,  203. 
Carpus:  Necturus,  85;  frog,  127;  tur- 
tle, 156;  pigeon,  203;  cat,  270. 
Cartilage,  anteorbital :  Necturus,  91. 

arytenoid:  Necturus,  68;  frog,  97; 
turtle,  138, 145 ;  pigeon,  187  ;  cat, 
246. 

basibranchial :  dogfish,  31;  Nectu- 
rus, 88. 

basihyal:  dogfish,  31. 

ceratobranchial :  dogfish,  31;  Nec- 
turus, 88. 

ceratohyal :  dogfish,  30 ;  Necturus, 
88. 

cricoid  :  pigeon,  187  ;  cat,  246. 

crico-thyroid :  turtle,  145. 

epibranchial :  dogfish,  31 ;  Necturus, 
88. 

epicoracoid :  frog,  126. 

extrabranchial :  dogfish,  31. 

hyoid:  dogfish,  8;  frog,  97,  130; 
turtle,  152. 

hyomandibular :  dogfish,  30. 

hypobranchial :  dogfish,  31. 

hypohyal :  Necturus,  88. 

labial :  dogfish,  30. 

Meckel's:  dogfish,  30;  perch,  58; 
Necturus,  88;  frog,  131;  turtle, 
152;  pigeon,  210. 


Cartilage,  paraglenoid :  frog,  126. 
pharyngobranchial :  dogfish,  31. 
procoracoid:  Necturus,  84;  frog, 

126;  turtle,  156. 
procricoid :  pigeon,  187. 
pterygoquadrate :  dogfish,  30. 
quadrate:  Necturus,  91. 
suprascapular :  frog,  126. 
thyroid :  cat,  246. 

Cat,  213. 

Cauda  epididymis :  cat,  229. 

Cauda  equina :  cat,  265. 

Central  nervous  system:  dogfish,  12, 
16 ;  perch,  41 ;  Necturus,  73 ;  frog, 
107 ;  turtle,  146 ;  pigeon,  188 ;  cat, 
246,  257. 

Centrum :  dogfish,  27 ;  perch,  55 ;  Nec- 
turus, 92;  frog,  129;  turtle,  150, 
151 ;  pigeon,  205 ;  cat,  272. 

Cerebellum:  dogfish,  16;  perch,  46; 
Necturus,  74;  frog,  111;  turtle, 
164 ;  pigeon,  194 ;  cat,  258. 

Cerebrum:  dogfish,  16;  perch,  46; 
Necturus,  74;  frog,  110;  turtle, 
163 ;  pigeon,  194  ;  cat,  267. 

Cervix  uteri :  cat,  231. 

Chondrocranium :  perch,  61 ;  Necturus, 
87. 

Chordae  tendinae:  pigeon,  185;  cat, 
241. 

Choroid  coat :  dogfish,  14 ;  perch,  43 ; 
pigeon,  192 ;  cat,  254. 

Ciliary  body  :  cat,  254. 

Clasper :  dogfish,  3,  32. 

Clavicle:  frog,  126;  pigeon,  202;  cat, 
270. 

Clei thrum :  perch,  64. 

Clitoris:  cat,  231. 

Cloaca:  dogfish,  3,  8,  11;  Necturus, 
67,  70,  72 ;  frog,  96, 99, 107  ;  turtle, 
137, 143, 146 ;  pigeon,  177, 178, 179. 

Cochlea:  cat,  256. 

Colon :  dogfish,  9 ;  turtle,  144 ;  cat, 
222,  226. 

Color :  dogfish,  2 ;  perch,  33 ;  Necturus, 
66 ;  frog,  94 ;  turtle,  136 ;  pigeon, 
167;  cat,  214. 

Columella:  frog,  133;  turtle,  148; 
pigeon,  193,  209. 


286 


VEBTEBKATE  ZOOLOGY 


Condyle :  dogfish,  29 ;  turtle,  153. 
Conjunctiva:  dogfish,  13;  perch,  42; 

pigeon,  191 ;  cat,  252. 
Conus  arteriosus :  dogfish,  6 ;  Necturus, 

70. 

Copula :  see  Bone,  basibranchial. 
Coracoid:    perch,  64;    Necturus,  84; 

frog,  126 ;  turtle,  156 ;  pigeon,  202. 
Cornea :  dogfish,  13 ;  perch,  42  ;  pigeon, 

190 ;  Cat,  252. 
Cornua  of  hyoidbone :  frog,  131 ;  turtle, 

152 ;  pigeon,  212 ;  cat,  245. 
Corpora  cavernosa :  cat,  230. 
Corpora  lutea :  cat,  230. 
Corpora  quadrigemina :  cat,  263,  265. 
Corpus  callosum  :  cat,  262. 
spongiosum :  cat,  230. 
striatura:  perch,  49;  pigeon,  197; 

cat,  264. 

Cortical  substance  of  kidney :  cat,  228. 
Costal  plates :  turtle,  136,  150. 
Cranium :  dogfish,  28  ;  perch,  66,  60 ; 

Necturus,  87,  89 ;  frog,  130,  131 ; 

turtle,  152  ;  pigeon,  207,  211;  cat, 

274. 
Cranium  proper :  perch,  61 ;  Necturus, 

89 ;  frog,  132 ;  turtle,  155 ;  pigeon, 

211 ;  cat,  275. 
Cribriform  plate :  cat,  278. 
Crista  ventralis :  frog,  127. 
Crop:  pigeon,  169. 
Cruciate  sulcus :  cat,  258. 
Crura  cerebri :  Necturus,  76 ;  frog,  114 ; 

turtle,  165. 

Crura  penis :  cat,  230. 
Crystalline  lens:  dogfish,  14;  perch, 

43 ;  pigeon,  192 ;  cat,  254. 

Deltoid  ridge :  pigeon,  202 ;  cat,  270. 
Dental  formula :  cat,  242. 
Descending  colon  :  cat,  223. 
Diaphragm :  cat,  219,  234. 
Digestive  system :   dogfish,  8 ;  perch, 

38 ;  Necturus,  70 ;  frog,  99 ;  turtle, 

143;  pigeon,  174,  177;  cat,  221, 

225. 
Digits :  Necturus,  85 ;  frog,  127  ;  turtle, 

157;  pigeon,  203,  204;  cat,  217, 

270,  272. 


Divisions  of  appendages :  Necturus,  67 ; 

frog,  96 ;  turtle,  137  ;  pigeon,  170, 

202,204;  cat,  217. 
Dogfish,  1. 

Duct,  accessory  pancreatic :  cat,  224. 
bile :  dogfish,  8 ;  perch, 40 ;  Necturus, 

71 ;  frog,  100 ;  turtle,  144 ;  pigeon, 

175 ;  cat,  224. 
common  bile :  cat,  224. 
Cuvierian:  dogfish,  21;  perch,  52; 

Necturus,  80. 
cystic :  cat,  224. 
endolymphatic :  dogfish,  15;  perch, 

46 ;  Necturus,  73. 
Ley  dig's :  dogfish,  11 ;  Necturus,  72 ; 

frog,  106. 
Miillerian:   dogfish,   11;   Necturus, 

72;  frog,  106. 
nasolachrymal :  cat,  252. 
pancreatic :    dogfish,   8 ;   frog,   101 ; 

turtle,  144 ;  pigeon,  175 ;  cat,  224. 
thoracic :  cat,  239. 
Wolffian :    dogfish,    10 ;    Necturus, 

71 ;  frog,  105. 
Ductus    Botalli:    turtle,     163;     cat, 

237. 
Duodenum :    dogfish,    9 ;    perch,    40 ; 

Necturus,   70 ;   frog,   100 ;   turtle, 

144;  pigeon,  174,  177;  cat,  222, 

226. 
Dura  mater :  cat,  267. 

Ear:  dogfish,  15;  perch,  44;  Necturus, 
73;  frog,  133;  turtle,  148;  pigeon, 
168,  193;  cat,  215,  255. 

Eardrum  :  see  Tympanic  membrane. 

Ectosylvian  gyrus :  cat,  258. 

Ectosylvian  sulcus :  cat,  258. 

Elasmobranchian  fish,  1. 

Endoskeleton :  dogfish,  26;  perch,  55; 
Necturus,  83;  frog,  125;  turtle, 
149 ;  pigeon,  200,  201 ;  cat,  268. 

Entoplastron :  turtle,  150. 

Epididymis:  dogfish,  11;  turtle,  146; 
cat,  228,  229. 

Epiglottis :  ca*t,  244,  246. 

Epiphysis :  see  Pineal  body. 

Epiplastron:  turtle,  150. 

Episternum :  frog,  126. 


INDEX 


287 


Eustachian  tube :  frog,  97;  turtle,  148,; 

pigeon,   172,   193,  207;  cat,  245, 

256. 
Exoskeleton:  dogfish,  26;  perch,  54; 

Necturus,  83;  frog,   125;   turtle, 

149 ;  pigeon,  200 ;  cat,  268. 
External    auditory    meatus :    pigeon, 

193;  cat,  255,  275. 
External  ear :  cat,  255. 
External  nares :  see  Nostrils. 
Extremities :  see  Appendages. 
Eyelids:  dogfish,  2;  frog,  95;  turtle, 

137 ;  pigeon,  168 ;  cat,  215,  251. 
Eyes:  dogfish,  2,  13;  perch,  34,  42; 

Necturus,    66;    frog,    95;    turtle, 

137;  pigeon,  168,  190;  cat,  215, 

251. 

Falciform  ligament :  pigeon,  174. 

Fallopian  tube :  cat,  230. 

False  diaphragm :  dogfish,  4 ;  perch, 
37. 

False  vocal  cords :  cat,  246. 

Fascia  lata :  cat,  267. 

Fascia,  lumbodorsal :  cat,  226. 

Fat  body  :  frog,  99,  107. 

Feathers :  pigeon,  166,  167,  200. 
contour:  pigeon,  166,  200. 
down :  pigeon,  167,  201. 
pin :  pigeon,  167,  201. 

Felis  maniculata,  214. 

Female  genital  organs:  dogfish,  11; 
perch,  41  ;  Necturus,  72 ;  frog, 
106;  turtle,  145;  pigeon,  179; 
cat,  230. 

Femur :  Necturus,  86 ;  frog,  128 ;  tur- 
tle, 157;  pigeon,  204;  cat,  271. 

Fenestra  ovalis :  frog,  133 ;  turtle,  148 ; 
pigeon,  193,  209 ;  cat,  256. 

Fenestra  rotunda:  pigeon,  209;  cat, 
256. 

Fibula:  Necturus,  86;  turtle,  167; 
pigeon,  204;  cat,  271. 

Filoplumes:  see  Feathers,  pin. 

Filum  terminale :  cat,  265. 

Fimbria :  cat,  264. 

Fin :  dogfish,  3,  31 ;  perch,  35,  63. 
anal :  see  Fin,  ventral, 
caudal :  dogfish,  3, 31 ;  perch,  35,  63. 


Fin,  dorsal:  dogfish,  3,  31;  perch,  35, 

63. 
median:  dogfish,  3,  31;  perch,  35, 

63. 

paired  :  dogfish,  3,  31 ;  perch,  35,  63. 
pectoral :  dogfish,  3,  32 ;  perch,  35, 

63. 
pelvic:   dogfish,   3,   32;   perch,  35, 

63. 
ventral:  dogfish,  3,  31;  perch,  35, 

63. 

Fin  rays :  dogfish,  32 ;  perch,  63,  64. 
Fishes :  dogfish,  1 ;  perch,  33. 
Foramen,  abducens :  dogfish,  29. 
anterior  ophthalmic :  dogfish,  29. 
atlantal :  cat,  273. 
glossopharyngeal :  dogfish,  29. 
hypoglossal :  cat,  278. 
iliosciatic :  pigeon,  204. 
inferior  dental :  cat,  280. 
infraorbital :  cat,  277. 
intervertebral :    frog,  108;    pigeon, 

206 ;  cat,  247,  272. 
lachrymal :  cat,  277. 
obturator:  Necturus,  86;  pigeon, 

204 ;  cat,  271. 
oculomotor:  dogfish,  29. 
optic:    dogfish,    29;    pigeon,    210; 

cat,  277. 

palatine:  cat,  277. 
pneumatic :  pigeon,  202. 
posterior  ophthalmic  :  dogfish,  29. 
sphenopalatine :  cat,  277. 
stylomastoid :  cat,  277. 
supracondyloid :  cat,  270. 
trigeminal :  dogfish,  29 ;  pigeon,  209. 
trochlear :  dogfish,  29. 
vagus:  dogfish,  29. 
Foramen  coracoideum :  Necturus,  84. 
Foramen  jugale :  cat,  278. 
Foramen  magnum:  dogfish,  28;  perch, 
61 ;  Necturus,  89 ;  frog,  131 ;  tur- 
tle, 153;  pigeon,  208;  cat,  275. 
Foramen  of    Monro :    Necturus,    77 ; 

frog,  114;  pigeon,  197;  cat,  264. 
Foramen  ovale  :  cat,  277. 
Foramen  rotundum :  cat,  277. 
Foramen  transversarium :  cat,  273. 
Foramen  triosseum :  pigeon,  202. 


288 


VERTEBRATE  ZOOLOGY 


Foramina  incisa :  cat,  275. 
Fore  legs  :  Necturus,    67 ;    frog,    96 ; 
turtle,  137;  pigeon,  171;  cat,  217, 
270. 

Fornix  :  cat,  262,  264. 
Fossa,  glenoid  :  dogfish,  32  ;  Necturus, 
84;  frog,  126  ;  turtle,  156  ;  pigeon, 
202 ;  cat,  269,  278. 
infraspinous :  cat,  269. 
olecranon :  cat,  270. 
supraspinous ;  cat,  269. 
temporal :  turtle,  153 :  cat,  275. 
Fossa  ovalis:  cat,  241. 
Fossa  rhomboidalis :  dogfish,  16 ;  Nec- 
turus, 75;  frog,  111. 
Frenulum  :  cat,  243,  244. 
Frog,  94. 

Frontal  organ :  frog,  95,  110. 
Fundus :  cat,  222. 

Gall  bladder:  dogfish,  5;  perch,  40; 
Necturus,  71 ;  frog,  98 ;  turtle,  144  ; 
cat,  219,  223. 

Ganglion,  anterior  cervical:  cat,  250. 
cceliac :  cat,  251. 

Gasserian :  Necturus,  75  ;  frog,  111 ; 
turtle,  164 ;  pigeon,  195 ;  cat,  259. 
jugal:  frog,  113. 
mesenteric:  cat,  251. 
middle  cervical :  cat,  250. 
posterior  cervical :  cat,  250. 
prootic:  frog,  112. 
semilunar :  cat,  251. 
spinal :  frog,  108 ;  pigeon,  188. 
Ganglion  jugulare  :  cat,  260. 
Ganglion  nodulosum :  cat,  260. 
Genital    organs:   dogfish,  10;    perch, 
40;  Necturus,  72;  frog,  106;  tur- 
tle, 145;  pigeon,  178;  cat,  228. 
Genital  pore :  perch,  41. 
Genu :  cat,  262. 
Gill  clefts :  see  Gill  slits, 
filaments  :  dogfish,  8 ;  perch,  35,  39. 
rakers :  perch,  35,  39. 
rays :  dogfish,  30 ;  perch,  60. 
slits:  dogfish,  2,  7;  perch,  35,  39; 

Necturus,  66,  68. 

Gills:  dogfish,  2,  8;  perch,  35,  39; 
Necturus,  66,  68. 


Gizzard  :  pigeon,  174,  177. 
Gland,  carotid :  frog,  120. 

Cowper's :  cat,  230. 

Harderian :  pigeon,  191. 

inf raorbital :  cat,  242. 

lachrymal :  pigeon,  191 ;  cat,  252. 

lymph :  cat,  224. 

Meibomian :  cat,  251. 

molar:  cat,  242. 

parotid :  cat,  242. 

prostate :  cat,  229. 

pseudothyroid :  frog,  116. 

rectal :  dogfish,  9. 

salivary :  cat,  242. 

shell :  dogfish,  11. 

sublingual :  cat,  242. 

submaxillary :  cat,  242. 

thymus:    frog,    116;    turtle,    141; 
pigeon,  180 ;  cat,  219,  234. 

thyroid:    frog,    116;    turtle,     141; 
pigeon,  180 ;  cat,  239. 

uropygial:  pigeon,  170. 
Glandular  stomach :  pigeon,  177. 
Glans  penis :  cat,  230. 
Glenoid  cavity :  see  Fossa,  glenoid. 
Glenoid  fossa :  see  Fossa,  glenoid. 
Glottis :  Necturus,  68 ;  frog,  97 ;  turtle, 
138;  pigeon,  172,  187;   cat,  244, 
245. 

Graafian  follicles :  cat,  230. 
Greater  tuberosity :  cat,  270. 
Great  omentum  :  pigeon,  174 ;  cat,  219, 

221. 

Great  trochanter :  pigeon,  204 ;  cat,  271. 
Gyri  of  brain :  cat,  257. 
Gyrus,  ectosylvian :  cat,  258. 

marginal :  cat,  258. 

orbital :  cat,  258. 

posterior :  cat,  258. 

sigmoid :  cat,  258. 

suprasylvian :  cat,  258. 

sylvian :  cat,  258. 

Hair :  cat,  214,  268. 

Hammer :  see  Malleus. 

Hard  palate :  cat,  243. 

Head :  dogfish,  2 ;  perch,  34 ;  Necturus, 

66 ;  frog,  96 ;  turtle,  137  ;  pigeon, 

168 ;  cat,  215. 


INDEX 


289 


Head  kidney :  perch,  41. 

Heart:  dogfish,  6,  20;  perch,  38,  49; 

Necturus,  69;   frog,   101;   turtle, 

139,  140;  pigeon,  175,  179,  184; 

cat,  220,  224,  235,  240. 
Hemispheres:  dogfish,  16;  perch,  46; 

Necturus,  74;   frog,   110;   turtle, 

163 ;  pigeon,  194 ;  cat,  257. 
Hepatic   portal  system :    dogfish,  20 ; 

perch,    49;    Necturus,    78;    frog, 

118;  turtle,  159;  pigeon,  176. 
Hilus :  cat,  227. 
Hind  legs:    Necturus,  67;   frog,  96; 

turtle,  137;  pigeon,  171 ;  cat,  217, 

271. 

Horn  of  ventricle :  cat,  264. 
Horns  of  hyoid  :  see  Cornua  of  hyoid. 
Horns  of  uterus :  cat,  230. 
Humerus:   Necturus,    85;    frog,    127; 

turtle,  156 ;  pigeon,  202 ;  cat,  270. 
Hyobranchial  apparatus :  Necturus,  88. 
Hyoid  apparatus:  frog,  130;  turtle, 

152;  pigeon,  212;  cat,  245. 
Hyoplastron:  turtle,  151. 
Hypophysis:   dogfish,  19;  perch,  48; 

Necturus,  88;  frog,  114;  turtle, 

165 ;  pigeon,  196 ;  cat,  261. 
Hypoplastron :  turtle,  151. 

Ileum :  cat,  222,  226. 

Ilium :  Necturus,  85 ;  frog,  128 ;  turtle, 

157  ;  pigeon,  203 ;  cat,  271. 
Incus:  cat,  256. 

Inferior  umbilicus :  pigeon,  200. 
Infraspinous  fossa:  cat,  269. 
Infundibulum :  dogfish,  19 ;  perch,  48 ; 

Necturus,   76;   frog,   113;  turtle, 

165;  pigeon,  196. 
Inner  ear:    dogfish,   15;    perch,   45; 

Necturus,  73 ;  turtle,  148 ;  pigeon, 

193 ;  cat,  256. 

Insertion  of  muscles :  frog,  122. 
Integumental  sense  organs:    dogfish, 

12 ;  perch,  42. 

Internal  auditory  meatus :  cat,  278. 
Internal  organs :  dogfish,  4 ;  perch,  36 ; 

Necturus,  68 ;  frog,  98 ;  turtle,  138 ; 

pigeon,  173;  cat,  218. 
Interorbital  septum :  pigeon,  209. 


Intestine  :  dogfish,  5,  9;  perch,  38,  40; 

Necturus,  70 ;  frog,  98, 100 ;  turtle, 

140,  143;  pigeon,  174,  177;   cat, 

222. 
Iris:  dogfish,  13;  perch,  42;  pigeon, 

191 ;  cat,  252. 
Ischium  :  frog,  128 ;  turtle,  157 ;  pigeon, 

203 ;  cat,  271. 

Jaws :  dogfish,  8 ;  perch,  39 ;  Necturus, 
68;  frog,  96;  turtle,  138;  pigeon, 
168;  cat,  215. 

Jejunum:  cat,  222. 

Keel :  pigeon,  207. 

Kidneys :  dogfish,  10 ;  perch,  41 ;  Nec- 
turus, 71;  frog,  105;  turtle,  146; 
pigeon,  178 ;  cat,  226. 

Lagena:    perch,    45;    Necturus,    74; 

pigeon,  194. 
Lambdoidal  crest:  pigeon,  208;  cat, 

275. 
Lambdoidal   ridge:    see   Lambdoidal 

crest. 

Lamina  terminalis :  cat  262. 
Large  intestine :  Necturus,    70 ;   frog, 
100 ;  turtle,  144 ;  pigeon,  177 ;  cat, 
222. 
Larynx :  turtle,  145 ;  pigeon,  186 ;  cat, 

245. 

Lateral  ligaments  of  bladder:  cat,  228. 
Lateral  line:    dogfish,   2,   12;  perch, 

33,  42. 

Lateral  sulcus :  cat,  258. 
Left  auricle:  Necturus,  70,  77;  frog, 

102,  115;  turtle,  142. 
Legs:  Necturus,  67;  frog,  96;  turtle, 

137;  pigeon,  171,  203;  cat,  217. 
Lesser  tuberosity :  cat,  270. 
Ligament,  falciform  :  pigeon,  174. 
lateral,  of  bladder :  cat,  228. 
suspensory,  of  bladder  :  cat,  228. 
suspensory,  of  eye :  cat,  254. 
suspensory,  of  liver :  cat,  221,  223. 
transverse :  cat,  273. 
Ligamentum  Botalli :  cat,  237. 
ovarii :  cat,  230. 
uteri :  cat,  230. 


290 


VEBTEBRATE  ZOOLOGY 


Limbs :  see  Legs. 

Linea  alba :  Necturus,  82  ;  frog,  123 ; 
pigeon,  198 ;  cat,  266. 

Lips :  Necturus,  66 ;  frog,  95 ;  cat,  215, 
243. 

Liver :  dogfish,  5, 8 ;  perch,  38, 40;  Nec- 
turus, 69,  70 ;  frog,  98,  100 ;  tur- 
tle, 139,  143;  pigeon,  174,  175; 
cat,  219,  221,  223. 

Lobi  inferiores :  dogfish,  19 ;  perch,  48. 

Lorenzinian  ampulla :  dogfish,  12,  18. 

Lower  jaw:  dogfish,  30;  perch,  57; 
Necturus,  87;  frog,  131;  turtle, 
152;  pigeon,  210;  cat,  280. 

Lumbar  region :  cat,  216. 

Lumbodorsal  fascia :  cat,  266. 

Lungs :  Necturus,  73 ;  frog,  99 ;  turtle, 
145;  pigeon,  173,  185;  cat,  219, 
246. 

Lymph  vessels :  pigeon,  175;  cat,  224. 

Male  genital  organs:  dogfish,  11; 
perch,  40;  Necturus,  72;  frog, 
106;  turtle,  145;  pigeon,  178; 
cat,  228. 

Malleus :  cat,  264. 

Mammals,  213. 

Mandible :  see  Lower  jaw. 

Manubrium :  cat,  273. 

Manus:  cat,  270. 

Marginal  gyrus :  cat,  258. 

Marginal  plates :  turtle,  136,  150. 

Maxilla :  see  Bone,  maxillary. 

Mediastinum :  cat,  220. 

Medulla  oblongata :  dogfish,  16 ;  perch, 
46;  Necturus,  74;  frog,  111;  tur- 
tle, 164 ;  pigeon,  194 ;  cat,  258. 

Medullary  substance :  cat,  228. 

Membrane,  alar:  pigeon,  172. 
branchiostegal :  perch,  35. 
nictitating :   dogfish,  2 ;  turtle,  137 ; 

pigeon,  168;  cat,  215,  251. 
semilunar:  pigeon,  186. 
tympanic :  frog,  95, 133 ;  turtle,  137, 
148 ;  pigeon,  193,  209 ;  cat,  255. 

Membranous  labyrinth :  see  Inner  ear. 

Mesentery:  dogfish,  5,  8;  perch,  40; 
Necturus,  69;  frog,  99;  turtle, 
144 ;  pigeon,  174 ;  cat,  220. 


Mesopterygium :  dogfish,  32. 
Metapterygium :  dogfish,  32. 
Midbrain :  see  Optic  lobes. 
Middle  commissure :  cat,  263,  265. 
Middle  ear :  see  Tympanic  cavity. 
Mouth:   dogfish,   2,  7,  8;   perch,  34, 
38;    Necturus,  66,  68,  70;    frog, 
95,  96,  99;  turtle,  137,  138,  143; 
pigeon,  168,  172;  cat,  215,  242. 
Muscle,  abdominal :  frog,  123 ;  pigeon, 

198,  199;  cat,  268. 
acromiodeltoid :  cat,  267. 
acromiotrapezius :  cat,  266. 
adductor  magnus :  frog,  124. 
biceps :  pigeon,  199 ;  cat,  268. 
biceps  femoris :  frog,  124 ;  cat,  267. 
body:  dogfish,  25;  perch,  53;  Nec- 
turus, 82. 

broncho-tracheal :  pigeon,  186,  187. 
ceratohyoid:  Necturus,  82. 
ciliary :  pigeon,  192 ;  cat,  254. 
clavobrachial :  cat,  266. 
clavotrapezius :  cat,  266. 
coraco-radial :  frog,  123. 
cubitocarpalis    profundus :    pigeon, 

199. 

cutaneous:  cat,  265. 
deltoid :  frog,  123. 
extensor  carpi  ulnaris :  pigeon,  199. 
extensor  radialis :  pigeon,  199. 
external  oblique :  frog,  124 ;  pigeon, 

199;  cat,  266,  268. 
external  rectus :  dogfish,  14 ;  perch, 

43;  pigeon,  191;  cat,  252. 
femoral :  Necturus,  83. 
femoro-tibialis :  pigeon,  199. 
flexor  carpi  ulnaris :  pigeon,  199. 
gastrocnemius :   frog,  124;   pigeon, 

200. 

geniohyoid :  Necturus,  82. 
gracilis :  cat,  268. 
great  cutaneous :  cat,  266. 
ilio-tibialis:  pigeon,  199. 
inferior  oblique :  dogfish,  14 ;  perch, 

43;  pigeon,  191;  cat,  252. 
inferior  rectus :  dogfish,  14 ;  perch, 

43 ;  pigeon,  191 ;  cat,  253. 
internal  oblique:  pigeon,  199;  cat, 
268. 


INDEX 


291 


Muscle,  internal  rectus:  dogfish,  14; 

perch,  43;  pigeon,  191;  cat,  253. 
latissimus  dorsi :  cat,  266. 
levator  scapulae:  cat,  267. 
masseter:  cat,  267. 
of  eyeball :   dogfish,  13 ;  perch,  43 ; 

pigeon,  191 ;  cat,  252. 
pectoral:   Necturus,  82;   frog,  122, 

123 ;  turtle,  139 ;  pigeon,  169, 198 ; 

cat,  267. 

pelvic:  turtle,  139. 
peroneus :  frog,  125. 
platysma :  cat,  266. 
procoraco-humeralis :  Necturus,  82. 
pronator  brevis :  pigeon,  199. 
pronator  longus :  pigeon,  199. 
pubo-ischio-f emoralis :  pigeon,  200. 
pyramidal:  pigeon,  192. 
pyriform :  Necturus,  83. 
quadrate:  pigeon,  192. 
rectus  abdominis :  frog,  123;  pigeon, 

199 ;  cat,  268. 

rectus  anticus  femoris :  frog,  124. 
rectus  internus  major :  frog,  124. 
rectus  internus  minor :  frog,  124. 
retractor :  turtle,  146 ;  pigeon,  188 ; 

cat,  252. 
sartorius:   frog,  124;   pigeon,  199; 

cat,  267. 
semimembranosus :  frog,  125 ;  pigeon, 

200. 

semitendinosus :  pigeon,  200. 
spinodeltoid :  cat,  266. 
sternomastoid :  cat,  267. 
subhyoid:  frog,  122. 
submandibular :  Necturus,  82 ,  frog, 

122;  pigeon,  199. 
superior  oblique :  dogfish,  13;  perch, 

43 ;  pigeon,  191 ;  cat,  252. 
superior  rectus :  dogfish,  13 ;  perch, 

43 ;  pigeon,  191 ;  cat,  253. 
temporal :  cat,  267. 
tibialis :  pigeon,  200. 
tibialis  anticus :  frog,  124. 
tracheo-sternal :  pigeon,  180,  187. 
transversus :  frog,  124 ;  pigeon,  199 ; 

cat,  268. 

trapezius :  cat,  266. 
triceps:  pigeon,  199;  cat,  267,  268. 


Muscle,  triceps  extensor  femoris :  frog, 

124 ;  cat,  267. 
vastus  externus :  frog,  124. 
vastus  internus :  frog,  124. 
Muscular  system  :  dogfish,  24 ;  perch, 

53;     Necturus,    82;     frog,     122; 

pigeon,  197;  cat,  265. 
Mustelus  canis,  1. 
Myocomma:   dogfish,  25;  perch,  53; 

Necturus,  82. 
Myomere :  see  Myotome. 
Myotome:    dogfish,    25;    perch,    53; 

Necturus,  82. 

Nasal  capsule :  dogfish,  28 ;  perch,  62 ; 
Necturus,  90;  frog,  133;  turtle, 
156;  pigeon,  190,  211;  cat,  244, 
251,  275,  279. 
Nasal  septum :  cat,  245. 
Nasopharynx :  cat,  244. 
Neck :  turtle,  137 ;  pigeon,  169 ;  cat, 215. 
Necturus,  65. 

Nerve,  abducens :  dogfish,  18 ;  perch, 
47  ;  frog,  112 ;  turtle,  164 ;  pigeon, 
195;  cat,  259. 

auditory:  dogfish,  18;  perch,  47; 
Necturus,  75;  frog,  112;  turtle, 
164 ;  pigeon,  196 ;  cat,  259. 

axillary :  cat,  248. 

caudal  spinal :  cat,  250. 

cranial:  dogfish,  12,  17;  perch,  41, 
46;  Necturus,  73,  75;  frog,  107, 
111 ;  turtle,  146,  163;  pigeon,  188, 
194 ;  cat,  247,  253. 

crural:  frog,  108. 

facial :  dogfish,  18 ;  perch,  47 ;  Nec- 
turus, 75;  frog,  112;  turtle,  164; 
pigeon,  196 ;  cat,  259. 

femoral :  cat,  249. 

genitofemoral :  cat,  249. 

glossopharyngeal:  dogfish,  18;  perch, 
47;  Necturus,  75;  frog,  113; 
pigeon,  196 ;  cat,  260. 

great  sciatic  :  cat,  249. 

great  splanchnic :  cat,  251. 

hyoid  branch  of  facial :  dogfish,  18. 

hyomandibular :  frog,  112. 

hypoglossal:  turtle,  165;  pigeon, 
196 ;  cat,  260. 


292 


VEETEBEATE  ZOOLOGY 


Nerve,  iliohypogastric :  frog,  108. 

intercostal :  cat,  248. 

lateral  cutaneous :  cat,  249. 

lateral  line :  dogfish,  19. 

lumbar  spinal :  cat,  248. 

mandibular  branch  of  trigeminal : 
dogfish,  18 ;  perch,  47 ;  turtle,  164 ; 
pigeon,  195;  cat,  259. 

maxillary  branch  of  trigeminal:  dog- 
fish, 18;  perch,  47;  turtle,  164; 
pigeon,  195 ;  cat,  259. 

maxillo-mandibular :  Necturus,  75; 
frog,  112. 

median :  cat,  247. 

musculo-cutaneous :  cat,  248. 

obturator:  cat,  249. 

oculomotor:  dogfish,  17;  perch,  46; 
Necturus,  75;  frog,  112;  turtle, 
164 ;  pigeon,  195 ;  cat,  259. 
.olfactory:  dogfish,  17;  perch,  46; 
Necturus,  75;  frog,  111;  turtle, 
164;  cat,  258. 

ophthalmic  branch  of  facial:  dog- 
fish, 18. 

ophthalmic  branch  of  trigeminal: 
dogfish,  17 ;  perch,  47 ;  Necturus, 
75;  frog,  112;  turtle,  164;  pigeon, 
195;  cat,  259. 

optic :  dogfish,  14, 17 ;  perch,  44, 46 ; 
Necturus,    75;   frog,   112;  turtle, 
164;  pigeon,  195;  cat,  258,  261. 
.  palatine  branch  of  facial:  dogfish, 
.       18;  frog,  112. 

pathetic :  see  Nerve,  trochlear. 

phrenic :  cat,  248. 

pneumogastric :  see  Nerve,  vagus. 

radial :  cat,  247. 

sacral  spinal :  cat,  249. 

saphenous:  cat,  249. 

sciatic :  frog,  108 ;  pigeon,  189 ;  cat, 
249. 

spinal :  dogfish,  12 ;  perch,  41 ;  Nec- 
turus, 73,  76;  frog,  107;  turtle, 
146 ;  pigeon,  188 ;  cat,  247,  265. 

spinal  accessory:  turtle,  165;  pigeon, 
196;  cat,  260. 

splanchnic  :  frog,  109 ;  cat,  251. 

subscapular :  cat,  248. 

suprascapular :  cat,  248. 


Nerve,  sympathetic:  see  Sympathetic 

.nervous  system. 
thoracic  spinal:  cat,  248. 
trigeminal:  dogfish,  17;  perch,  47; 
Necturus,   75;   frog,   112;   turtle, 
164 ;  pigeon,  195 ;  cat,  259. 
trochlear:   dogfish,   17;   perch,  47; 
frog,    112;    turtle,    164;    pigeon, 
195 ;  cat,  259. 
ulnar :  cat,  247. 

vagus :  dogfish,  19 ;  perch,  47 ;  Nec- 
turus, 75;  frog,  113;  turtle,  165; 
pigeon,  180,  196 ;  cat,  260. 
Nervous  system:  dogfish,  12;  perch, 
41 ;  Necturus,  73 ;  frog,  107  ;  tur- 
tle, 146 ;  pigeon,  188 ;  cat,  246. 
central :  see  Central  nervous  system, 
peripheral:  see  Peripheral  nervous 

system. 

sympathetic:  see  Sympathetic  ner- 
vous system. 

Neural  plates :  turtle,  136. 
Neural  spine :  dogfish,  27 ;  perch,  55 ; 
Necturus,  92;  frog,   129;  pigeon, 
205;  cat,  272. 

Nictitating  membrane :  dogfish,  2 ;  tur- 
tle, 137;  pigeon,  168;  cat,  215, 
251. 

Nipples :  cat,  216. 
Nose :  cat,  215,  251. 
Nostrils:  dogfish,  2;  perch,  35;  Nec- 
turus, 66;  frog,  95;  turtle,   137; 
pigeon,  168,  190 ;  cat,  245,  275. 
Notochord:  dogfish,    27;    perch,    55; 

Necturus,  92. 
Nuchal  plates :  turtle,  136,  150. 

Occipital  condyle :  Necturus,  89 ;  frog, 
132 ;  turtle,  153 ;  pigeon,  208 ;  cat, 
275. 

(Esophagus :  dogfish,  8 ;  perch,  39 ; 
Necturus,  70;  frog,  100;  turtle, 
144 ;  pigeon,  177 ;  cat,  219,  245. 

Olecranon  fossa :  cat,  270. 

Olfactory  lobes:  dogfish,  16;  perch, 
46;  frog,  110;  turtle,  163;  pigeon, 
194;  cat,  257,  261. 

Olfactory  organ  :  see  Nasal  capsule. 

Olfactory  tracts :  cat,  261. 


INDEX 


293. 


Operculum  :  perch,  35,  59. 
Operculum  of  ear :  Necturus,  91 ;  frog, 

133. 

Optic  capsule :  perch,  61 ;  Necturus, 
90 ;  frog,  133 ;  turtle,  156  j  pigeon, 
211;  cat,  251,  276. 

Optic  chiasma :  perch,  46,  48 ;  frog, 
113;  turtle,  165;  pigeon,  195;  cat, 
258,  261. 

Optic  commissure :  pigeon,  197. 
Optic  lobes :   dogfish,  16 ;   perch,  46 ; 
Necturus,  74;    frog,    110;  turtle, 
163;  pigeon,  194;  cat,  257. 
Optic   thalamus  :    frog,    112 ;  pigeon, 

197 ;  cat,  262,  264. 

Optic  tracts :  pigeon,  195 ;  cat,  261,  265. 
Ora  serrata :  cat,  255. 
Orbit  of  eye :  dogfish,  29 ;  perch,  61 ; 
turtle,  153 ;  pigeon,  209 ;  cat,  275. 
Orbital  fissure  :  cat,  277. 
Orbital  gyrus :  cat,  258. 
Organ  of  Jacobson :  cat,  243. 
Origin  of  muscles  :  frog,  122. 
Ostium :  cat,  230. 
Otolith :  perch,  45 ;  Necturus,  74. 
Ovary :    dogfish,    5,    10 ;    perch,    41 ; 
Necturus,   72;  frog,  106;   turtle, 
145;  pigeon,  179;  cat,  230. 
Oviduct:  dogfish,  5,  11;  Necturus,  72; 
frog,    106-;    turtle,    146;    pigeon, 
179;  cat,  230. 

• 

Palate :  cat,  243. 

Pancreas:  dogfish,  5,  8;  perch,  40; 
Necturus,  69,  70 ;  frog,  100 ;  tur- 
tle, 144;  pigeon,  174;  cat,  221, 
224. 

Pancreas  Aselli :  cat,  224. 
Papilla,  circumvallate  :  cat,  244. 
filiform  :  cat,  244. 
fungiform :  cat,  244. 
urinary  :  dogfish,  3,  11. 
rirogenital :  dogfish,  3,  10. 
Paraphysis  :  frog,  110. 
Patella:  pigeon,  204;  cat,  271. 
Pectoral  girdle  :  dogfish,  3,  32  ;  perch, 
36,  64 ;  Necturus,  83  ;  frog,  125 ; 
turtle,  156 ;  pigeon,  201 ;  cat,  269. 
Peduncles:  pigeon,  197. 


Pedunculi  cerebri :  cat,  261. 
Pelvic  girdle :  dogfish,  3,  32 ;  Necturus, 
85 ;  frog,  127 ;  turtle,  167 ;  pigeon, 
203;  cat,  271. 
Pelvis  of  kidney :  cat,  227. 
Penis :  turtle,  145 ;  cat,  230. 
Perch,  33. 

Pericardial  cavity:  dogfish,  4,  6; 
perch ;  37,  49 ;  Necturus,  69  ;  frog, 
99;  turtle,  139;  pigeon,  174;  cat, 
221. 

Pericardium:    dogfish,  4;  perch,    37; 
Necturus,    69;    frog,  99;    turtle, 
139 ;  pigeon,  174 ;  cat,  220. 
Periorbita:  cat,  251. 
Peripheral  nervous  system :  dogfish,  12 ; 
perch,  41 ;  Necturus,  73 ;  frog,  107 ; 
turtle,  146 ;  pigeon,  188 ;  cat,  247. 
Peritoneum  :   dogfish,    4 ;   perch,   37 ; 
Necturus,  69 ;  frog,  99 ;  turtle,  139 ; 
pigeon,  174  ;  cat,  220. 
Pes:  cat,  271. 
Pessulus:  pigeon,  187. 
Petrous  portion  of  temporal :  cat,  277. 
Phalanges:  Necturus,    85,    87;    frog, 
127  ;  turtle,  157 ;  pigeon,  203,  204 ; 
cat,  270,  272. 

Pharynx  :  dogfish,  7  ;  perch,  38  ;  Nec- 
turus, 68;  frog,   96;  turtle,  138; 
pigeon,  172 ;  cat,  242,  244. 
Pia  mater :  cat,  257. 
Pigeon,  166. 

Pigeon's  milk :  pigeon,  169. 
Pigment  of  eye  :  dogfish,  14 ;  perch,  43; 

pigeon,  192 ;  cat,  254. 
Pillars  of  the  fauces :  cat,  243. 
Pillars  of  the  fornix  :  cat,  264. 
Pineal  body:  dogfish,  16;  perch,  46; 
Necturus,   74;   frog,   110;  turtle, 
163 ;  pigeon,  194 ;  cat,  263. 
Pituitary  body  :  see  Hypophysis. 
Plantar  aponeurosis  :  frog,  124. 
Plastron :  turtle,  136,  150. 
Plates,  costal :  turtle,  136,  150. 
marginal:  turtle,  136,  150. 
neural :  turtle,  136. 
nuchal :  turtle,  136,  150. 
pygal :  turtle,  136,  150. 
vertebral :  turtle,  150. 


294 


VERTEBRATE  ZOOLOGY 


Pleura :  pigeon,  185 ;  cat,  219. 
Plexus,   anterior  choroid:    frog,  111; 

cat,  263. 

anterior  gastric  :  cat,  260. 
brachial:    frog,    108;    turtle,    147; 

pigeon,  188 ;  cat,  247. 
cardiac :  cat,  251,  260. 
carotid :  cat,  240. 
choroid:  frog,  111;  turtle,  164;  cat, 

263. 

lumbar:  pigeon,  189. 
lumbo-sacral :  turtle,  147 ;  cat,.  249. 
posterior  choroid :  frog,  111 ;  cat,  263. 
posterior  gastric :  cat,  260. 
pudendus:  pigeon,  189. 
pulmonary :  cat,  260. 
sacral:  pigeon,  189. 
sciatic:  frog,  108. 
solar :  pigeon,  191 ;  cat,  233,  251. 
Pons :  cat,  258. 
Portal  system :  cat,  225. 
Posterior  cornua:   frog,  131;  pigeon, 

212;  cat,  245. 

Posterior  extremities:   Necturus,  85; 
frog,   127;    turtle,    157;    pigeon, 
203;  cat,  216,  271. 
Posterior  gyrus :  cat,  258. 
Posterior  nares :  Necturus,  68 ;   frog, 
97 ;  turtle,  138 ;  pigeon,  172,  190 ; 
cat,  245. 

Postzygapophyses :  perch,  55 ;  frog, 
129 ;  turtle,  151 ;  pigeon,  205 ;  cat, 
272. 

Premaxilla :  see  Bone,  preinaxillary. 
Prepuce :  cat,  230. 
Presylvian  sulcus  :  cat,  258. 
Prezygapophyses :  perch,  55 ;  frog,  129 ; 
turtle,  151 ;  pigeon,  205 ;  cat,  272. 
Primary  quills :  pigeon,  170. 
Process,  acromion :  cat,  269. 
ciliary :  pigeon,  192. 
coracoid:  cat,  269. 
coronary :  turtle,  152. 
coronoid :  cat,  280. 
ensiform :  cat,  273. 
epiotic :  perch,  62. 
frontal :  cat,  276. 

haemal :  dogfish,  27 ;  perch,  55 ;  cat, 
274. 


Process,  intercalary :  dogfish,  27. 
maxillary :  pigeon,  208. 
rnetacromion :  cat,  269. 
nasal :  pigeon,  208. 
neural :  dogfish,  27 ;  perch,  55 ;  Nec- 
turus, 92  ;  frog,  129 ;  pigeon,  205  ; 
cat,  272. 
odontoid  :  turtle,  151 ;  pigeon,  206 ; 

cat,  273. 
olecranon  :  Necturus,  85 ;  frog,  127 ; 

pigeon,  203 ;  cat,  270. 
palatine :  pigeon,  208. 
parotic :  perch,  62. 
pterygoid :  cat,  277. 
spinous :  see  Neural  spine, 
'transverse:    dogfish,  27;   Necturus, 
92 ;  frog,  129 ;  turtle,  151 ;  pigeon, 
205 ;  cat,  272. 
uncinate :  pigeon,  207. 
xiphoid :  pigeon,  207. 
zygomatic,    of   frontal   bone:    cat, 

276. 
zygomatic,  of  maxillary  bone:  cat, 

276. 
zygomatic,     of     squamosal     bone : 

pigeon,  209;  cat,  276,  277. 
zygomatic,  of  temporal  bone:   cat, 

276,  277. 
Processus    f alciformis :     dogfish,    15  ; 

perch,  44. 

Propterygium :  dogfish,  32. 
Pseudobranct :  perch,  35. 
Pubis :  frog,  128 ;  turtle,  157 ;  pigeon, 

203 ;  cat,  271. 

Pubo-ischium :  Necturus,  85. 
Pupil  of  eye:  dogfish,  13;  perch,  42; 

pigeon,  190. 

Pygal  plate :  turtle,  136,  150. 
Pygostyle :  pigeon,  206. 
Pyloric  appendages :  perch,  38,  40. 
Pyramidal  tracts:  cat,  261. 
Pyriform  lobe :  cat,  258. 

Quill :  pigeon,  200. 

Radio-ulna:  frog,  127. 

Radius:    Necturus,    85;    turtle,    156; 

pigeon,  203 ;  cat,  270. 
Rectal  diverticula :  pigeon,  177. 


INDEX 


295 


Rectum :  dogfish,  4,  9 ;  perch,  40 ;  frog, 

100;  turtle,  144;  pigeon,  177;  cat, 

223. 
Regions  of  spine :  dogfish,  27 ;  perch, 

65 ;  Necturus,  92 ;  frog,  129;  turtle, 

149;  pigeon,  205;  cat,  272. 
Renal  portal  system :  dogfish,  21 ;  Nec- 
turus, 78;  frog,  118;  turtle,  159; 

pigeon,  176. 
Reptiles,  135. 
Respiratory    system:    Necturus,    73; 

frog,  97  ;  turtle,  145 ;  pigeon,  185 ; 

cat,  244. 
Restiform  bodies :  dogfish,  17 ;  perch, 

46. 
Retina :  dogfish,  14 ;  perch,  43 ;  pigeon, 

192;  cat,  254. 
Ribs :  dogfish,  28  ;  perch,  56  ;  Necturus, 

93 ;  turtle,  150,  151 ;  pigeon,  206 ; 

cat,  273. 
Right  auricle :  Necturus,  70,  77 ;  frog, 

102,115;  turtle,  142;  pigeon,  184; 

cat,  235,  237. 

Rostrum  of  brain :  cat,  262. 
Rostrum  of  skull :  dogfish,  28 ;  pigeon, 

209,  210. 

Sac,  abdominal:  pigeon,  173. 
air:  pigeon,  169,  173,  185. 
anterior  thoracic :  pigeon,  173. 
axillary :  pigeon,  173. 
cervical :  pigeon,  173. 
interclavicular :  pigeon,  173. 
omental :  cat,  221. 
pleural :  cat,  219. 
posterior  thoracic :  pigeon,  173. 
vocal :  frog,  95. 
Sacculus:    perch,   45;    Necturus,    73; 

pigeon,  194. 
Sacral  region :  cat,  216. 
Sacrum  :  Necturus,  86  ;  frog,  128 ;  tur- 
tle, 150;  pigeon,  206;  cat,  271,  274. 
Sagittal  fissure :  frog,  110 ;  cat,  257. 
Sagittal  ridge  :  cat,  275. 
Scales,  ctenoid :  perch,  33,  54. 

placoid :  dogfish,  2,  26. 
Scapula:    perch,    64;    Necturus,    84; 
frog,    126;    turtle,    166;    pigeon, 
202 ;  cat,  269. 


Sclera :  see  Sclerotic  coat. 

Sclerotic  coat :  dogfish,  13 ;  perch,  43 ; 
pigeon,  190 ;  cat,  254. 

Secondary  quills :  pigeon,  170. 

Sella  turcica :  cat,  278. 

Semilunar  membrane :  pigeon,  186. 

Semilunar  notch :  cat,  270. 

Semilunar  tendon  :  cat,  235. 

Seminal  vescicle :  dogfish,  11 ;  frog, 
106;  pigeon,  178. 

Seminiferous  tubules :  cat,  229. 

Septum  nasi :  pigeon,  190. 

Septum  pellucidum  :  cat,  262. 

Shaft :  pigeon,  200. 

Shell :  turtle,  136. 

Shoulder  girdle  :  see  Pectoral  girdle. 

Sigmoid  gyrus :  cat,  258. 

Silvery  layer :  perch,  44. 

Sinus,  anterior  cardinal:  dogfish,  21. 
frontal :  cat,  279. 
hepatic :  dogfish,  21. 
of  kidney  :  cat,  228. 
posterior  cardinal :  dogfish,  21. 
sphenoid :  cat,  279. 
venosus :  dogfish,  6 ;  perch,  38,  50 ; 
Necturus,  70;    frog,  101;  turtle, 
140. 
urogenital :  see  Vestibule,  genital. 

Skate,  1. 

Skeletal  system:  dogfish,  26;  perch, 
54;  Necturus,  83;  frog,  125;  tur- 
tle, 149;  pigeon,  200;  cat,  268. 

Skin:  dogfish,  26;  perch,  54;  Nectu- 
rus, 65;  frog,  95;  turtle,  136; 
pigeon,  171. 

Skull :  dogfish,  28 ;  perch,  56 ;  Nectu- 
rus, 87;  frog,  130;  turtle,  152; 
pigeon,  207 ;  cat,  274. 

Small  intestine :  perch,  40 ;  Necturus, 
70 ;  frog,  100 ;  turtle,  144 ;  pigeon, 
177 ;  cat,  222. 

Soft  palate  :  cat,  243. 

Special  sense  capsules:  dogfish,  28; 
perch,  61 ;  Necturus,  90 ;  frog,  133 ; 
turtle,  156;  pigeon,  211;  cat,  275. 

Special  sense  organs :  dogfish,  12 ; 
perch,  41,  42;  Necturus,  73;  frog, 
107 ;  turtle,  146, 148 ;  pigeon,  188, 
190;  cat,  247,  251. 


296 


VEKTEBRATE  ZOOLOGY 


Spermatic  cord  :  cat,  229. 

Spinal  column :  dogfish,  25,  27  ;  perch, 

54,  55;  Necturus,  92;  frog,  129; 

,  turtle,  149 ;  pigeon,  204 ;  cat,  272. 
Spinal  cord:   dogfish,  12,  19;   perch, 

41,   48;   Necturus,    73,  76;  frog, 

107, 109 ;  turtle,  146 ;  pigeon,  188 ; 

cat,  265. 

Spine  of  scapula:  cat,  269. 
Spiracle :  dogfish,  2,  7. 
Spleen :  dogfish,  5 ;  perch,  38 ;  Nectu- 
rus,  69;   frog,   100;  turtle,   144; 

pigeon,  177 ;  cat,  221. 
Splenium :  cat,  262. 
Squalus  acanthias,  1. 
Squainous  portion  of  temporal:   cat, 

277.' 

Stapes :  pigeon,  193,  209 ;  cat,  256. 
Sternum :    Necturus,    84 ;    frog,    126 ; 

pigeon,  207 ;  cat,  273. 
Stirrup :  see  Stapes. 
Stomach :  dogfish,  5,  9 ;  perch,  38,  39 ; 

Necturus,   69,    70;   frog,   98,  99; 

turtle,  140,  144 ;  pigeon,  174,  177 ; 

cat,  221,  226. 

Substantia  perforata  anterior :  cat,  261. 
Substantia  perforata  posterior:    cat, 

261. 

Sulci  of  brain ;  cat,  257. 
Sulcus,  ectosylvian :  cat,  258. 
lateral :  cat,  258. 
presylviau  :  cat,  258. 
suprasylvian :  cat,  258. 
Superior  umbilicus :  pigeon,  200. 
Supracleithrum :  perch,  64. 
Supraorbital  ridge :  cat,  275. 
Suprarenal  body  :  see  Adrenal  body. 
Supraspinous  fossa :  cat,  269. 
Suprasylvian  gyrus :  cat,  258. 
Suprasylvian  sulcus :  cat,  258. 
Suspensorium :  dogfish,  30;  perch,  57; 

Necturus,  91;    frog,  134;    turtle, 

155 ;  pigeon,  209. 
Suspensory  ligament  of  bladder:  cat, 

228. 

Suspensory  ligament  of  eye :  cat,  254. 
Suspensory  ligament  of  liver :  cat,  221, 

223. 
Sylvian  gyrus :  cat,  258. 


Sympathetic  nervous  system :  dogfish, 
12 ;  perch,  41 ;  Necturus,  73 ;  frog, 
107, 109 ;  turtle,  146 ;  pigeon,  188, 
189 ;  cat,  250. 

Symphysis  pubis :  cat,  271. 

Synsacrum :  pigeon,  206. 

Syrinx:  pigeon,  186. 

Table  of  frogs,  94. 

Table  of  reptiles,  135. 

Tail :  dogfish,  2 ;  perch,  35 ;  Necturus, 
66;  turtle,  137;  pigeon,  168,  170; 
cat,  215,  217. 

Tapetum  lucidum :  dogfish,  14 ;  perch, 
44 ;  cat,  254. 

Tarso-metatarsus :  pigeon,  204. 

Tarsus :  Necturus,  86 ;  frog,  128 ;  tur- 
tle, 157;  pigeon,  204;  cat,  271. 

Teeth:  dogfish,    2,   8,  26;  perch,  39, 
58;    Necturus,    68,  87;  frog,  97, 
131,  134;  cat,  215,  242,  274. 
canine :  cat,  242. 
incisor:  cat,  242. 
maxillary :  perch,  39 ;  frog,  97. 
molar :  cat,  242. 
premolar:  cat,  242. 
vomerine :  perch,  39 ;  frog,  97. 

Teleostean  fish,  33. 

Temporal  fossa :  turtle,  153 ;  cat,  275. 

Tendon  of  Achilles :  frog,  124. 

Tentorium :  cat,  278. 

Testes;  dogfish,  5,  10;  perch,  40; 
Necturus,  72;  frog,  106;  turtle, 
145 ;  pigeon,  178 ;  cat,  228,  229. 

Thalamencephalon  :  dogfish,  16 ;  perch, 
46;  Necturus,  74;  frog,  110;  tur- 
tle, 163;  pigeon,  194. 

Thoracic  cavity  :  cat,  219,  221,  234. 

Thorax  -.  pigeon,  169 ;  cat,  216. 

Thyrocervical  axis  :  cat,  239. 

Tibia:  Necturus,  86;  turtle.  157; 
pigeon,  204  ;  cat,  271. 

Tibio-fibula :  frog,  128. 

Tibio-tarsus :  pigeon,  204. 

Toad,  94. 

Tongue:  dogfish,  8;  perch,  39;  Nec- 
turus, 68;  frog,  96;  turtle,  138; 
pigeon,  172 ;  cat,  244. 

Tonsils:  cat,  243. 


INDEX 


297 


Torus :  perch,  48. 

Trachea:  turtle,  141,  145;  pigeon, 
185 ;  cat,  219,  245. 

Transverse  colon :  cat,  222. 

Transverse  ligament :  cat,  273 

Trapezium :  cat,  259,  261. 

Truncus  arteriosus :  Necturus,  70. 

Trunk:  dogfish,  2;  perch,  35;  Nec- 
turus, 66;  frog,  95;  turtle,  137; 
pigeon,  168,  169;  cat,  215,  216. 

Tuber  cinereum:  cat,  261. 

Tuberculum :  pigeon,  206 ;  cat,  273. 

Turbinals :  pigeon,  190 ;  cat,  245,  278. 

Turtle,  135. 

Tympanic  bulla :  cat,  275. 

Tympanic  cavity:  frog,  133;  turtle, 
148 ;  pigeon,  193,  208 ;  cat,  255. 

Tympanic  membrane:  frog,  95,  133; 
turtle,  137,  148 ;  pigeon,  193,  209 ; 
cat,  255. 

Tympanic  portion  of  temporal:  cat,  277. 

Tympanum  of  syrinx :  pigeon,  186. 

Ulna:  Necturus,  85;  turtle,  156; 
pigeon,  203 ;  cat,  270. 

Upper  jaw:  dogfish,  30;  perch,  58; 
Necturus,  91 ;  frog,  134 ;  turtle, 
152;  pigeon,  211;  cat,  280. 

Ureter:  dogfish,  11;  perch,  41;  Nec- 
turus, 71;  frog,  105;  turtle,  146; 
pigeon,  178 ;  cat,  227. 

Urethra :  cat,  227. 

Urinary  bladder :  perch,  41 ;  Necturus, 
72;  frog,  99,  105;  turtle,  140, 145; 
cat,  219,  227. 

Urinary  organs:  dogfish,  10;  perch, 
41 ;  Necturus,  71 ;  frog,  105;  tur- 
tle, 146  ;  pigeon,  178 ;  cat,  226. 

Urinary  pore :  perch,  41. 

Urodelan  amphibians,  65. 

Urogenital  system :  dogfish,  10 ;  perch, 
40 ;  Necturus,  71 ;  frog,  105 ;  tur- 
tle, 145 ;  pigeon,  178 ;  cat,  226. 

Uropygium:  pigeon,  170. 

Urostyle :  perch,  56 ;  frog,  129. 

Uterus :  dogfish,  11 ;  Necturus,  72 ; 
frog,  106 ;  turtle,  146 ;  cat,  230. 

Utriculus :  perch,  45 ;  Necturus,  73 ; 
pigeon,  194. 


Vagina :  cat,  231. 

Valve,  bicuspid :  pigeon,  185 ;  cat,  241. 

branchiostegal :  perch,  39. 

ileocolic :  cat,  226. 

mitral:  pigeon,  185;  cat,  241. 

oral:  perch,  39. 

pyloric:  cat,  226. 

semilunar:  frog,  103;  pigeon,  185; 
cat,  241. 

spiral :  dogfish,  9 ;  frog,  103. 

tricuspid:  cat,  241. 
Vane :  pigeon,  200. 
Vasdeferens:  turtle,  145;  pigeon,  178; 

cat,  228,  229. 

Vasa  efferentia:  dogfish,  11;  Necturus, 
72 ;  frog,  106 ;  turtle,  145 ;  cat,  229. 
Vascular  layer :  perch,  44. 
Vascular  system :  dogfish,  20 ;  perch, 
49 ;  Necturus,  77  ;  frog,  114 ;  turtle, 
158;  pigeon,  175, 179 ;  cat,  224, 231. 
Vein,   abdominal:  Necturus,  77,  78; 
frog,  118;  turtle,  158. 

adipose:  frog,  117. 

adrenolumbalis :  cat,  232. 

anterior  cardinal:  perch,  52;  Nec- 
turus, 80. 

anterior  facial :  cat,  239. 

anterior  mesenteric:  pigeon,  176; 
cat,  225. 

anterior  renal :  pigeon,  182,  183. 

axillary :  cat,  238. 

azygos:  cat,  237. 

brachial:  frog,  117;  pigeon,  181; 
cat,  238. 

caudal :  dogfish,  21  ;  perch,  52 ; 
Necturus,  79;  turtle,  159;  pigeon, 
176 ;  cat,  232. 

caval:  Necturus,  71;  frog,  115;  tur- 
tle, 158,  161;  pigeon,  176;  cat, 
225,  231. 

common  iliac :  cat,  231. 

coronary :  cat,  237. 

costocervical :  cat,  238. 

deep  femoral :  cat,  232. 

dorsolumbar :  frog,  119. 

epigastric :  cat,  232. 

external  iliac :  frog,  119;  cat,  232. 

external  jugular :  Necturus,  80  ; 
frog,  116;  cat,  238. 


298 


VERTEBRATE   ZOOLOGY 


Vein,  femoral:  Necturus,  78;  frog, 
119;  turtle,  159;  pigeon,  182;  cat, 
232. 

gastric:  perch,  49;  Necturus,  78; 
frog,  118 ;  turtle,  160. 

gastroduodenal :  frog,  118;  pigeon, 
176. 

gastrosplenic :  cat,  225. 

genital:  Necturus,  79;  frog,  117; 
turtle,  161. 

hepatic:  perch,  52;  Necturus,  79; 
frog,  117  ;  turtle,  141, 161 ;  pigeon, 
182 ;  cat,  232. 

hepatic  portal:  dogfish,  20;  perch, 
49;  Necturus,  78;  frog,  118;  tur- 
tle, 158,  159 ;  pigeon,  176. 

hypogastric :  see  Vein,  internal  iliac. 

iliac :  dogfish,  21 ;  pigeon,  182 ;  cat, 
231. 

iliolumbalis :  cat,  232. 

inferior  mesenteric:  see  Vein,  pos- 
terior inesenteric. 

innominate:  frog,  116;  cat,  238. 

intercostal :  cat,  237. 

internal  iliac :  pigeon,  176,  182 ;  cat, 
232. 

internal  jugular :  Necturus,  80 ;  frog, 
116;  turtle,  161 ;  cat,  238. 

internal  mammary :  pigeon,  181 ; 
cat,  238. 

internal  mandibular :  frog,  116. 

intestinal :  perch,  49,  53 ;  Necturus, 
78;  frog,  118. 

jugular:  perch,  52;  Necturus,  80; 
frog,  116;  pigeon,  180,  181;  cat, 
238. 

lateral :  dogfish,  21 ;  Necturus,  80. 

left  pelvic  :  frog,  118. 

lef t  precaval :  frog,  115;  turtle,  141, 
161 ;  pigeon,  181. 

left  pulmonary  :  Necturus,  80 ;  frog, 
119;  turtle,  142;  pigeon,  181. 

left  renal  portal :  pigeon,  176. 

lingual :  frog,  116. 

mesenteric:  Necturus,  71,  78;  tur- 
tle, 160 ;  cat,  225. 

ovarian  :  frog,  117  ;  cat,  232. 

pancreatic:  frog,  118;  turtle,  160. 

"pelvic :  Necturus,  78 ;  frog,  119. 


Vein,  phrenic :  cat,  232. 

pneumatocystic :  perch,  49. 

portal :  dogfish,  20 ;  perch,  49 ;  Nec- 
turus, 77;  frog,  117;  turtle,  158; 
pigeon,  176 ;  cat,  225. 

postcaval :  Necturus,  71,  79;  frog, 
102,  117  ;  turtle,  142, 161 ;  pigeon, 
181,  182 ;  cat,  231. 

posterior  cardinal :  perch,  52 ;  Nec- 
turus, 79. 

posterior  facial :  cat,  239. 

posterior  mesenteric:  pigeon,  176; 
cat,  225. 

precaval :  frog,  102, 115;  turtle,  141, 
161 ;  pigeon,  181 ;  cat,  236,  238. 

pulmonary  :  Necturus,  80 ;  frog,  119 ; 
turtle,  142,  158;  pigeon,  175;  cat, 
225,  237. 

renal:  dogfish,  22;  perch,  52;  frog, 
117 ;  turtle,  161  ;  cat,  231. 

renal  portal :  dogfish,  21 ;  Necturus, 
78;  frog,  119;  turtle,  158;  pigeon, 
182. 

right  pelvic  :  frog,  118. 

right  precaval:  frog,  115;  turtle, 
141,  161 ;  pigeon,  181. 

right  pulmonary :  Necturus,  80 ;  frog, 
119;  turtle,  142;  pigeon,  181. 

right  renal  portal :  pigeon,  176. 

sacralis  media:  see  Vein,  caudal. 

sciatic:  frog,  119. 

spermatic  :  frog,  117  ;  cat,  232. 

spinal :  perch,  52. 

splenic :  perch,  49 ;  Necturus,  78 ; 
frog,  118;  cat,  221. 

subclavian :  dogfish,  21;  perch,  53; 
Necturus,  80;  frog,  116,  117; 
turtle,  161;  cat,  238. 

subscapular:  frog,  116;  cat,  238. 

superior  mesenteric:  see  Vein,  ante- 
rior mesenteric. 

systemic:  dogfish,  21;  perch,  49; 
Necturus,  77,  79 ;  frog,  115 ;  turtle, 
158;  pigeon,  175;  cat,  225. 

transverse :  cat,  239. 

vertebral :  cat,  238. 
Veins :  dogfish,  20 ;  perch,  49,  52 ;  Nec- 
turus, 77;  frog,  114,  115;  turtle, 
158;  pigeon,  175;  cat,  225. 


INDEX 


299 


Ventricle  of  heart:  dogfish,  6;  perch, 
38,  50;  Necturus,  69;  frog,  101; 
turtle,  140;  pigeon,  175,  179;  cat, 
235. 

Ventricles     of     brain:    dogfish,     19; 
perch,  48 ;  Necturus,  76 ;  frog,  114 ; 
pigeon,  197 ;  cat,  26S,  265. 
Verinis :  cat,  258. 

Vertebra :  dogfish,  27 ;  perch,  55 ;  Nec- 
turus, 92;  frog,  129;  turtle,  150; 
pigeon,  205 ;  cat,  272. 
caudal :  dogfish,  28 ;  perch,  55 ;  Nec- 
turus, 93 ;  turtle,  151 ;  pigeon,  206 ; 
cat,  274. 

cervical:  Necturus,  92;  frog,  129; 
turtle,  151;  pigeon,  205;  cat, 
272. 

lumbar :  pigeon,  206 ;  cat,  274. 
sacral :    Necturus,    92 ;    frog,    130 ; 
turtle,  150 ;  pigeon,  206 ;  cat,  274. 
thoracic :  pigeon,  206 ;  cat,  273. 
thoraco-lumbar  :  Necturus,  92 ;  frog, 

129. 

Vertebral  column  :  see  Spinal  column. 
Vertebral  plates :  turtle,  150. 


Vestibule  of  ear:  dogfish,  15;  perch, 
45 ;  Necturus,  73 ;  cat,  256. 

Vestibule,  genital:  cat,  227,  231. 

VibrissEe :  see  Whiskers. 

Villi:  cat,  226. 

Visceral  skeleton:  dogfish,  28,  29; 
perch,  56,  57 ;  Necturus,  87 ;  frog, 
130;  turtle,  152,  155;  pigeon,  207; 
cat,  274,  276. 

Vitreous  humor:  dogfish,  14;  perch, 
44 ;  pigeon,  193 ;  cat,  255. 

Vocal  cords :  cat,  246. 

Vulva:  cat,  227,  231. 

Whiskers :  cat,  214,  268. 
Windpipe :  see  Trachea. 
Wing  coverts :  pigeon,  171. 
Wings :  pigeon,  170,  199,  201. 
Wrist :  see  Carpus. 

Xiphiplastron :  turtle,  151. 

Zygapophyses :  perch,  55;  Necturus, 
92 ;  frog,  129 ;  turtle,  151 ;  pigeon, 
205 ;  cat,  272. 


ANNOUNCEMENTS 


A  COURSE  IN 
INVERTEBRATE  ZOOLOGY 

A  Guide  to  the  Dissection  and  Comparative  Study  of 
Invertebrate  Animals 

By  HENRY  S.  PRATT,  Professor  of  Biology  in  Haverford  College,   Pa.,  and 

Instructor  in  Comparative  Anatomy  at  the  Marine  Biological  Laboratory 

at  Cold  Spring  Harbor,  Long  Island. 


8-vo.     Cloth,     xii  -\-  210  pages.     List  price,  $1.25 ;  mailing  price, 


THIS  book  has  been  written  for  use  in  colleges  and 
normal  schools.  It  contains  specific  directions  for 
the  dissection  of  thirty-four  invertebrate  animals. 
These  directions  are  very  full  and  have  been  arranged  with 
great  care  to  enable  the  student,  in  most  cases,  to  work  out 
a  dissection  with  a  single  animal. 

The  object  of  the  course  is  to  teach  comparative  anatomy. 
Each  of  the  larger  groups  of  invertebrates  is  studied  as  a 
whole,  instead  of  in  the  usual  detached  types  of  the  different 
groups.  By  this  method  the  attention  is  constantly  directed 
to  the  structural  features  which  characterize  the  entire  group 
under  consideration. 

A  classification  of  animals  based  upon  relationships  is 
given  in  an  appendix,  together  with  short  definitions  of  the 
groups  mentioned.  The  position  in  the  system  of  each  form 
studied  and  its  relationships  with  other  animals  may  thus  be 
kept  in  mind. . 


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THE  ELEMENTS  OF  GEOLOGY 

By  WILLIAM  HARMON  NORTON 

Professor  of  Geology  in  Cornell  College,  Mt.  Vernon,  Iowa 


8vo.     Cloth.     461  pages.      Illustrated.     List  price,  $1.40  J  mailing  price,  $1.55 


THE  essentials  of  the  science  of  geology  are  treated 
with  fullness  and  ample  illustration  in  this  text-book 
for  beginners.  By  limiting  his  discussion  chiefly  to  this 
continent  the  author  has  been  able  to  devote  a  large 
amount  of  space  to  the  principles  which  he  describes.  The 
following  characteristics  are  important. 

1.  The  outline  is  exceptionally  simple.    Under  the  leading  geological 
processes  are  grouped  the  rock  structures  and  land  forms  of  which 
they  are  the  cause. 

2.  The    inductive    method    is    emphasized    throughout.      Concrete 
examples  are  given  large  space  as  the  basis  of  generalizations  of  the 
science.     Numerous  exercises  and  problems,  many  of  which  are  in  the 
form  of  diagrams,  are   designed   to   train  the  pupil  and  to  test  his 
knowledge. 

3.  The  cycle  idea  is  made  prominent,  and  both  the  records  of  erosion 
and  those  of  sedimentation  are  given  special  attention. 

4.  In  historical  geology  a  broad  view  is  afforded  of  the  development 
of  the  North  American  continent  and  of  the  evolution  of  life  upon  the 
earth.     Only  the  leading  types  of  plants  and  animals  are  mentioned, 
and  special  attention  is  given  to  those  which  mark  the  lines  of  descent 
of  forms  now  living. 

The  book  is  designed  for  use  in  high  schools  and  acad- 
emies, and  may  also  be  found  useful  in  short  elementary 
college  courses. 


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BERGEN'S 
FOUNDATIONS  OF  BOTANY 

By  JOSEPH  Y.  BERGEN 

Recently  Instructor  in  Biology  in  the  English  High  School,  Boston 
and  Author  of  "  Elements  of  Botany  " 

412  +  257  pages.      Illustrated.     List  price,  $1.50  j  mailing  price,  $1.70 


A  HANDBOOK  FOR  THE  USE  OF  TEACHERS 

To  accompany  Bergen' s  Foundations  of  Botany 

Flexible  cloth.      64  pages.      List  price,  30  cents  ;  mailing  price,  35  cents 


ONE  of  the  notable  text-books  on  our  list  is  "  Foundations 
of  Botany  "  by  Mr.  Bergen,  whose  "  Elements  of  Botany  " 
has  come  to  be  the  most  widely  used  recent  text-book  on 
the  subject  in  the  higher  schools  and  academies  of  the  country. 

The  "  Foundations  of  Botany "  is  sufficient  to  prepare  for 
any  college  or  university  which  accepts  botany  as  an  entrance 
requirement.  It  offers  an  extended  and  comprehensive  course 
for  schools  that  wish  to  devote  an  entire  year  to  the  subject, 
and  provides  the  teacher  who  has  only  a  minimum  amount  of 
time  with  the  distinct  advantage  of  a  considerable  option  as 
regards  the  kind  and  amount  of  work  which  he  shall  present 
to  his  classes.  It  represents  the  simplest  and  most  practical 
methods  of  botany  teaching,  combining  a  standard  text  liberally 
illustrated  with  a  complete  course  in  laboratory  work  and  a  key 
for  the  study  of  systematic  botany. 

The  treatment  of  structural  and  physiological  botany  is 
unusually  full  and  yet  has  special  reference  to  the  necessary 
limitations  of  work  in  secondary  schools. 

The  flora  includes  seven  hundred  species,  and  is  the  only 
recent  short  and  thoroughly  usable  and  intelligible  flora  of  the 
central  and  northeastern  states.  The  descriptions  are  written  in 
the  very  simplest  language  consistent  with  scientific  accuracy. 


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ELECTRICITY,  SOUND,  AND 
LIGHT 

By  ROBERT  ANDREWS  MILLIKAN,  Associate  Professor  of  Physics  in 
The   University  of  Chicago,  and  JOHN  MILLS,    Instruc- 
tor in  Physics  in  Western  Reserve  University 


8vo.    Cloth.     389  pages.    Illustrated.    List  price,  $2.00.;  mailing  price,  $2.15 


THIS  book  represents  a  one-semester  college  course 
which  has  been  given  in  substantially  its  present  form 
for  a  number  of  years  in  The  University  of  Chicago,  Western 
Reserve  University,  and  several  other  similar  institutions. 

It  is  the  outgrowth  of  the  conviction  that  in  courses  of 
intermediate  grade  in  colleges,  universities,  and  engineering 
schools,  a  thorough  grasp  of  the  fundamental  principles  of 
physics  is  not  readily  gained  unless  theory  is  presented 
in  immediate  connection  with  related  concrete  laboratory 
problems.  It  represents  a  complete  logical  development, 
from  the  standpoint  of  theory  as  well  as  experiment,  of  the 
subjects  indicated  in  the  title. 

The  book  contains  twenty-eight  chapters,  —  sixteen  in 
electricity,  five  in  sound,  and  seven  in  light.  Each  chapter 
is  concluded  by  the  appropriate  experiment.  These  experi- 
ments have  been  put  into  such  form  that  they  demand  no 
special  apparatus  and  can  be  performed  by  students  in  the 
second  year  of  college  within  the  limited  time  of  a  two-hour 
laboratory  period.  "Electricity,  Sound,  and  Light"  may  be 
combined  with  "Mechanics,  Molecular  Physics,  and  Heat," 
by  Professor  Millikan,  to  form  the  texts  for  an  excellent 
course  of  one  year  in  college  physics. 


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